_content/doc: revert "temporarily add Go language specification documents"
Revert commit 2e3ad7d979299962a9e843e8eb77f28f337c37cb (CL 393115).
By now, the website is using Go content from release-branch.go1.18,
so this temporary mitigation is no longer needed.
Fixes golang/go#51686.
Change-Id: I47e3962cdffd88c708e1c150d9cf4bdcac217b24
Reviewed-on: https://go-review.googlesource.com/c/website/+/393355
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Trust: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
diff --git a/_content/doc/go1.17_spec.html b/_content/doc/go1.17_spec.html
deleted file mode 100644
index 390d93f..0000000
--- a/_content/doc/go1.17_spec.html
+++ /dev/null
@@ -1,6857 +0,0 @@
-<!--{
- "Title": "The Go Programming Language Specification",
- "Subtitle": "Version of Oct 15, 2021"
-}-->
-
-<h2 id="Introduction">Introduction</h2>
-
-<p>
-This is a reference manual for the Go programming language. For
-more information and other documents, see <a href="/">golang.org</a>.
-</p>
-
-<p>
-Go is a general-purpose language designed with systems programming
-in mind. It is strongly typed and garbage-collected and has explicit
-support for concurrent programming. Programs are constructed from
-<i>packages</i>, whose properties allow efficient management of
-dependencies.
-</p>
-
-<p>
-The grammar is compact and simple to parse, allowing for easy analysis
-by automatic tools such as integrated development environments.
-</p>
-
-<h2 id="Notation">Notation</h2>
-<p>
-The syntax is specified using Extended Backus-Naur Form (EBNF):
-</p>
-
-<pre class="grammar">
-Production = production_name "=" [ Expression ] "." .
-Expression = Alternative { "|" Alternative } .
-Alternative = Term { Term } .
-Term = production_name | token [ "…" token ] | Group | Option | Repetition .
-Group = "(" Expression ")" .
-Option = "[" Expression "]" .
-Repetition = "{" Expression "}" .
-</pre>
-
-<p>
-Productions are expressions constructed from terms and the following
-operators, in increasing precedence:
-</p>
-<pre class="grammar">
-| alternation
-() grouping
-[] option (0 or 1 times)
-{} repetition (0 to n times)
-</pre>
-
-<p>
-Lower-case production names are used to identify lexical tokens.
-Non-terminals are in CamelCase. Lexical tokens are enclosed in
-double quotes <code>""</code> or back quotes <code>``</code>.
-</p>
-
-<p>
-The form <code>a … b</code> represents the set of characters from
-<code>a</code> through <code>b</code> as alternatives. The horizontal
-ellipsis <code>…</code> is also used elsewhere in the spec to informally denote various
-enumerations or code snippets that are not further specified. The character <code>…</code>
-(as opposed to the three characters <code>...</code>) is not a token of the Go
-language.
-</p>
-
-<h2 id="Source_code_representation">Source code representation</h2>
-
-<p>
-Source code is Unicode text encoded in
-<a href="https://en.wikipedia.org/wiki/UTF-8">UTF-8</a>. The text is not
-canonicalized, so a single accented code point is distinct from the
-same character constructed from combining an accent and a letter;
-those are treated as two code points. For simplicity, this document
-will use the unqualified term <i>character</i> to refer to a Unicode code point
-in the source text.
-</p>
-<p>
-Each code point is distinct; for instance, upper and lower case letters
-are different characters.
-</p>
-<p>
-Implementation restriction: For compatibility with other tools, a
-compiler may disallow the NUL character (U+0000) in the source text.
-</p>
-<p>
-Implementation restriction: For compatibility with other tools, a
-compiler may ignore a UTF-8-encoded byte order mark
-(U+FEFF) if it is the first Unicode code point in the source text.
-A byte order mark may be disallowed anywhere else in the source.
-</p>
-
-<h3 id="Characters">Characters</h3>
-
-<p>
-The following terms are used to denote specific Unicode character classes:
-</p>
-<pre class="ebnf">
-newline = /* the Unicode code point U+000A */ .
-unicode_char = /* an arbitrary Unicode code point except newline */ .
-unicode_letter = /* a Unicode code point classified as "Letter" */ .
-unicode_digit = /* a Unicode code point classified as "Number, decimal digit" */ .
-</pre>
-
-<p>
-In <a href="https://www.unicode.org/versions/Unicode8.0.0/">The Unicode Standard 8.0</a>,
-Section 4.5 "General Category" defines a set of character categories.
-Go treats all characters in any of the Letter categories Lu, Ll, Lt, Lm, or Lo
-as Unicode letters, and those in the Number category Nd as Unicode digits.
-</p>
-
-<h3 id="Letters_and_digits">Letters and digits</h3>
-
-<p>
-The underscore character <code>_</code> (U+005F) is considered a letter.
-</p>
-<pre class="ebnf">
-letter = unicode_letter | "_" .
-decimal_digit = "0" … "9" .
-binary_digit = "0" | "1" .
-octal_digit = "0" … "7" .
-hex_digit = "0" … "9" | "A" … "F" | "a" … "f" .
-</pre>
-
-<h2 id="Lexical_elements">Lexical elements</h2>
-
-<h3 id="Comments">Comments</h3>
-
-<p>
-Comments serve as program documentation. There are two forms:
-</p>
-
-<ol>
-<li>
-<i>Line comments</i> start with the character sequence <code>//</code>
-and stop at the end of the line.
-</li>
-<li>
-<i>General comments</i> start with the character sequence <code>/*</code>
-and stop with the first subsequent character sequence <code>*/</code>.
-</li>
-</ol>
-
-<p>
-A comment cannot start inside a <a href="#Rune_literals">rune</a> or
-<a href="#String_literals">string literal</a>, or inside a comment.
-A general comment containing no newlines acts like a space.
-Any other comment acts like a newline.
-</p>
-
-<h3 id="Tokens">Tokens</h3>
-
-<p>
-Tokens form the vocabulary of the Go language.
-There are four classes: <i>identifiers</i>, <i>keywords</i>, <i>operators
-and punctuation</i>, and <i>literals</i>. <i>White space</i>, formed from
-spaces (U+0020), horizontal tabs (U+0009),
-carriage returns (U+000D), and newlines (U+000A),
-is ignored except as it separates tokens
-that would otherwise combine into a single token. Also, a newline or end of file
-may trigger the insertion of a <a href="#Semicolons">semicolon</a>.
-While breaking the input into tokens,
-the next token is the longest sequence of characters that form a
-valid token.
-</p>
-
-<h3 id="Semicolons">Semicolons</h3>
-
-<p>
-The formal grammar uses semicolons <code>";"</code> as terminators in
-a number of productions. Go programs may omit most of these semicolons
-using the following two rules:
-</p>
-
-<ol>
-<li>
-When the input is broken into tokens, a semicolon is automatically inserted
-into the token stream immediately after a line's final token if that token is
-<ul>
- <li>an
- <a href="#Identifiers">identifier</a>
- </li>
-
- <li>an
- <a href="#Integer_literals">integer</a>,
- <a href="#Floating-point_literals">floating-point</a>,
- <a href="#Imaginary_literals">imaginary</a>,
- <a href="#Rune_literals">rune</a>, or
- <a href="#String_literals">string</a> literal
- </li>
-
- <li>one of the <a href="#Keywords">keywords</a>
- <code>break</code>,
- <code>continue</code>,
- <code>fallthrough</code>, or
- <code>return</code>
- </li>
-
- <li>one of the <a href="#Operators_and_punctuation">operators and punctuation</a>
- <code>++</code>,
- <code>--</code>,
- <code>)</code>,
- <code>]</code>, or
- <code>}</code>
- </li>
-</ul>
-</li>
-
-<li>
-To allow complex statements to occupy a single line, a semicolon
-may be omitted before a closing <code>")"</code> or <code>"}"</code>.
-</li>
-</ol>
-
-<p>
-To reflect idiomatic use, code examples in this document elide semicolons
-using these rules.
-</p>
-
-
-<h3 id="Identifiers">Identifiers</h3>
-
-<p>
-Identifiers name program entities such as variables and types.
-An identifier is a sequence of one or more letters and digits.
-The first character in an identifier must be a letter.
-</p>
-<pre class="ebnf">
-identifier = letter { letter | unicode_digit } .
-</pre>
-<pre>
-a
-_x9
-ThisVariableIsExported
-αβ
-</pre>
-
-<p>
-Some identifiers are <a href="#Predeclared_identifiers">predeclared</a>.
-</p>
-
-
-<h3 id="Keywords">Keywords</h3>
-
-<p>
-The following keywords are reserved and may not be used as identifiers.
-</p>
-<pre class="grammar">
-break default func interface select
-case defer go map struct
-chan else goto package switch
-const fallthrough if range type
-continue for import return var
-</pre>
-
-<h3 id="Operators_and_punctuation">Operators and punctuation</h3>
-
-<p>
-The following character sequences represent <a href="#Operators">operators</a>
-(including <a href="#Assignments">assignment operators</a>) and punctuation:
-</p>
-<pre class="grammar">
-+ & += &= && == != ( )
-- | -= |= || < <= [ ]
-* ^ *= ^= <- > >= { }
-/ << /= <<= ++ = := , ;
-% >> %= >>= -- ! ... . :
- &^ &^=
-</pre>
-
-<h3 id="Integer_literals">Integer literals</h3>
-
-<p>
-An integer literal is a sequence of digits representing an
-<a href="#Constants">integer constant</a>.
-An optional prefix sets a non-decimal base: <code>0b</code> or <code>0B</code>
-for binary, <code>0</code>, <code>0o</code>, or <code>0O</code> for octal,
-and <code>0x</code> or <code>0X</code> for hexadecimal.
-A single <code>0</code> is considered a decimal zero.
-In hexadecimal literals, letters <code>a</code> through <code>f</code>
-and <code>A</code> through <code>F</code> represent values 10 through 15.
-</p>
-
-<p>
-For readability, an underscore character <code>_</code> may appear after
-a base prefix or between successive digits; such underscores do not change
-the literal's value.
-</p>
-<pre class="ebnf">
-int_lit = decimal_lit | binary_lit | octal_lit | hex_lit .
-decimal_lit = "0" | ( "1" … "9" ) [ [ "_" ] decimal_digits ] .
-binary_lit = "0" ( "b" | "B" ) [ "_" ] binary_digits .
-octal_lit = "0" [ "o" | "O" ] [ "_" ] octal_digits .
-hex_lit = "0" ( "x" | "X" ) [ "_" ] hex_digits .
-
-decimal_digits = decimal_digit { [ "_" ] decimal_digit } .
-binary_digits = binary_digit { [ "_" ] binary_digit } .
-octal_digits = octal_digit { [ "_" ] octal_digit } .
-hex_digits = hex_digit { [ "_" ] hex_digit } .
-</pre>
-
-<pre>
-42
-4_2
-0600
-0_600
-0o600
-0O600 // second character is capital letter 'O'
-0xBadFace
-0xBad_Face
-0x_67_7a_2f_cc_40_c6
-170141183460469231731687303715884105727
-170_141183_460469_231731_687303_715884_105727
-
-_42 // an identifier, not an integer literal
-42_ // invalid: _ must separate successive digits
-4__2 // invalid: only one _ at a time
-0_xBadFace // invalid: _ must separate successive digits
-</pre>
-
-
-<h3 id="Floating-point_literals">Floating-point literals</h3>
-
-<p>
-A floating-point literal is a decimal or hexadecimal representation of a
-<a href="#Constants">floating-point constant</a>.
-</p>
-
-<p>
-A decimal floating-point literal consists of an integer part (decimal digits),
-a decimal point, a fractional part (decimal digits), and an exponent part
-(<code>e</code> or <code>E</code> followed by an optional sign and decimal digits).
-One of the integer part or the fractional part may be elided; one of the decimal point
-or the exponent part may be elided.
-An exponent value exp scales the mantissa (integer and fractional part) by 10<sup>exp</sup>.
-</p>
-
-<p>
-A hexadecimal floating-point literal consists of a <code>0x</code> or <code>0X</code>
-prefix, an integer part (hexadecimal digits), a radix point, a fractional part (hexadecimal digits),
-and an exponent part (<code>p</code> or <code>P</code> followed by an optional sign and decimal digits).
-One of the integer part or the fractional part may be elided; the radix point may be elided as well,
-but the exponent part is required. (This syntax matches the one given in IEEE 754-2008 §5.12.3.)
-An exponent value exp scales the mantissa (integer and fractional part) by 2<sup>exp</sup>.
-</p>
-
-<p>
-For readability, an underscore character <code>_</code> may appear after
-a base prefix or between successive digits; such underscores do not change
-the literal value.
-</p>
-
-<pre class="ebnf">
-float_lit = decimal_float_lit | hex_float_lit .
-
-decimal_float_lit = decimal_digits "." [ decimal_digits ] [ decimal_exponent ] |
- decimal_digits decimal_exponent |
- "." decimal_digits [ decimal_exponent ] .
-decimal_exponent = ( "e" | "E" ) [ "+" | "-" ] decimal_digits .
-
-hex_float_lit = "0" ( "x" | "X" ) hex_mantissa hex_exponent .
-hex_mantissa = [ "_" ] hex_digits "." [ hex_digits ] |
- [ "_" ] hex_digits |
- "." hex_digits .
-hex_exponent = ( "p" | "P" ) [ "+" | "-" ] decimal_digits .
-</pre>
-
-<pre>
-0.
-72.40
-072.40 // == 72.40
-2.71828
-1.e+0
-6.67428e-11
-1E6
-.25
-.12345E+5
-1_5. // == 15.0
-0.15e+0_2 // == 15.0
-
-0x1p-2 // == 0.25
-0x2.p10 // == 2048.0
-0x1.Fp+0 // == 1.9375
-0X.8p-0 // == 0.5
-0X_1FFFP-16 // == 0.1249847412109375
-0x15e-2 // == 0x15e - 2 (integer subtraction)
-
-0x.p1 // invalid: mantissa has no digits
-1p-2 // invalid: p exponent requires hexadecimal mantissa
-0x1.5e-2 // invalid: hexadecimal mantissa requires p exponent
-1_.5 // invalid: _ must separate successive digits
-1._5 // invalid: _ must separate successive digits
-1.5_e1 // invalid: _ must separate successive digits
-1.5e_1 // invalid: _ must separate successive digits
-1.5e1_ // invalid: _ must separate successive digits
-</pre>
-
-
-<h3 id="Imaginary_literals">Imaginary literals</h3>
-
-<p>
-An imaginary literal represents the imaginary part of a
-<a href="#Constants">complex constant</a>.
-It consists of an <a href="#Integer_literals">integer</a> or
-<a href="#Floating-point_literals">floating-point</a> literal
-followed by the lower-case letter <code>i</code>.
-The value of an imaginary literal is the value of the respective
-integer or floating-point literal multiplied by the imaginary unit <i>i</i>.
-</p>
-
-<pre class="ebnf">
-imaginary_lit = (decimal_digits | int_lit | float_lit) "i" .
-</pre>
-
-<p>
-For backward compatibility, an imaginary literal's integer part consisting
-entirely of decimal digits (and possibly underscores) is considered a decimal
-integer, even if it starts with a leading <code>0</code>.
-</p>
-
-<pre>
-0i
-0123i // == 123i for backward-compatibility
-0o123i // == 0o123 * 1i == 83i
-0xabci // == 0xabc * 1i == 2748i
-0.i
-2.71828i
-1.e+0i
-6.67428e-11i
-1E6i
-.25i
-.12345E+5i
-0x1p-2i // == 0x1p-2 * 1i == 0.25i
-</pre>
-
-
-<h3 id="Rune_literals">Rune literals</h3>
-
-<p>
-A rune literal represents a <a href="#Constants">rune constant</a>,
-an integer value identifying a Unicode code point.
-A rune literal is expressed as one or more characters enclosed in single quotes,
-as in <code>'x'</code> or <code>'\n'</code>.
-Within the quotes, any character may appear except newline and unescaped single
-quote. A single quoted character represents the Unicode value
-of the character itself,
-while multi-character sequences beginning with a backslash encode
-values in various formats.
-</p>
-
-<p>
-The simplest form represents the single character within the quotes;
-since Go source text is Unicode characters encoded in UTF-8, multiple
-UTF-8-encoded bytes may represent a single integer value. For
-instance, the literal <code>'a'</code> holds a single byte representing
-a literal <code>a</code>, Unicode U+0061, value <code>0x61</code>, while
-<code>'ä'</code> holds two bytes (<code>0xc3</code> <code>0xa4</code>) representing
-a literal <code>a</code>-dieresis, U+00E4, value <code>0xe4</code>.
-</p>
-
-<p>
-Several backslash escapes allow arbitrary values to be encoded as
-ASCII text. There are four ways to represent the integer value
-as a numeric constant: <code>\x</code> followed by exactly two hexadecimal
-digits; <code>\u</code> followed by exactly four hexadecimal digits;
-<code>\U</code> followed by exactly eight hexadecimal digits, and a
-plain backslash <code>\</code> followed by exactly three octal digits.
-In each case the value of the literal is the value represented by
-the digits in the corresponding base.
-</p>
-
-<p>
-Although these representations all result in an integer, they have
-different valid ranges. Octal escapes must represent a value between
-0 and 255 inclusive. Hexadecimal escapes satisfy this condition
-by construction. The escapes <code>\u</code> and <code>\U</code>
-represent Unicode code points so within them some values are illegal,
-in particular those above <code>0x10FFFF</code> and surrogate halves.
-</p>
-
-<p>
-After a backslash, certain single-character escapes represent special values:
-</p>
-
-<pre class="grammar">
-\a U+0007 alert or bell
-\b U+0008 backspace
-\f U+000C form feed
-\n U+000A line feed or newline
-\r U+000D carriage return
-\t U+0009 horizontal tab
-\v U+000B vertical tab
-\\ U+005C backslash
-\' U+0027 single quote (valid escape only within rune literals)
-\" U+0022 double quote (valid escape only within string literals)
-</pre>
-
-<p>
-All other sequences starting with a backslash are illegal inside rune literals.
-</p>
-<pre class="ebnf">
-rune_lit = "'" ( unicode_value | byte_value ) "'" .
-unicode_value = unicode_char | little_u_value | big_u_value | escaped_char .
-byte_value = octal_byte_value | hex_byte_value .
-octal_byte_value = `\` octal_digit octal_digit octal_digit .
-hex_byte_value = `\` "x" hex_digit hex_digit .
-little_u_value = `\` "u" hex_digit hex_digit hex_digit hex_digit .
-big_u_value = `\` "U" hex_digit hex_digit hex_digit hex_digit
- hex_digit hex_digit hex_digit hex_digit .
-escaped_char = `\` ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | `\` | "'" | `"` ) .
-</pre>
-
-<pre>
-'a'
-'ä'
-'本'
-'\t'
-'\000'
-'\007'
-'\377'
-'\x07'
-'\xff'
-'\u12e4'
-'\U00101234'
-'\'' // rune literal containing single quote character
-'aa' // illegal: too many characters
-'\xa' // illegal: too few hexadecimal digits
-'\0' // illegal: too few octal digits
-'\uDFFF' // illegal: surrogate half
-'\U00110000' // illegal: invalid Unicode code point
-</pre>
-
-
-<h3 id="String_literals">String literals</h3>
-
-<p>
-A string literal represents a <a href="#Constants">string constant</a>
-obtained from concatenating a sequence of characters. There are two forms:
-raw string literals and interpreted string literals.
-</p>
-
-<p>
-Raw string literals are character sequences between back quotes, as in
-<code>`foo`</code>. Within the quotes, any character may appear except
-back quote. The value of a raw string literal is the
-string composed of the uninterpreted (implicitly UTF-8-encoded) characters
-between the quotes;
-in particular, backslashes have no special meaning and the string may
-contain newlines.
-Carriage return characters ('\r') inside raw string literals
-are discarded from the raw string value.
-</p>
-
-<p>
-Interpreted string literals are character sequences between double
-quotes, as in <code>"bar"</code>.
-Within the quotes, any character may appear except newline and unescaped double quote.
-The text between the quotes forms the
-value of the literal, with backslash escapes interpreted as they
-are in <a href="#Rune_literals">rune literals</a> (except that <code>\'</code> is illegal and
-<code>\"</code> is legal), with the same restrictions.
-The three-digit octal (<code>\</code><i>nnn</i>)
-and two-digit hexadecimal (<code>\x</code><i>nn</i>) escapes represent individual
-<i>bytes</i> of the resulting string; all other escapes represent
-the (possibly multi-byte) UTF-8 encoding of individual <i>characters</i>.
-Thus inside a string literal <code>\377</code> and <code>\xFF</code> represent
-a single byte of value <code>0xFF</code>=255, while <code>ÿ</code>,
-<code>\u00FF</code>, <code>\U000000FF</code> and <code>\xc3\xbf</code> represent
-the two bytes <code>0xc3</code> <code>0xbf</code> of the UTF-8 encoding of character
-U+00FF.
-</p>
-
-<pre class="ebnf">
-string_lit = raw_string_lit | interpreted_string_lit .
-raw_string_lit = "`" { unicode_char | newline } "`" .
-interpreted_string_lit = `"` { unicode_value | byte_value } `"` .
-</pre>
-
-<pre>
-`abc` // same as "abc"
-`\n
-\n` // same as "\\n\n\\n"
-"\n"
-"\"" // same as `"`
-"Hello, world!\n"
-"日本語"
-"\u65e5本\U00008a9e"
-"\xff\u00FF"
-"\uD800" // illegal: surrogate half
-"\U00110000" // illegal: invalid Unicode code point
-</pre>
-
-<p>
-These examples all represent the same string:
-</p>
-
-<pre>
-"日本語" // UTF-8 input text
-`日本語` // UTF-8 input text as a raw literal
-"\u65e5\u672c\u8a9e" // the explicit Unicode code points
-"\U000065e5\U0000672c\U00008a9e" // the explicit Unicode code points
-"\xe6\x97\xa5\xe6\x9c\xac\xe8\xaa\x9e" // the explicit UTF-8 bytes
-</pre>
-
-<p>
-If the source code represents a character as two code points, such as
-a combining form involving an accent and a letter, the result will be
-an error if placed in a rune literal (it is not a single code
-point), and will appear as two code points if placed in a string
-literal.
-</p>
-
-
-<h2 id="Constants">Constants</h2>
-
-<p>There are <i>boolean constants</i>,
-<i>rune constants</i>,
-<i>integer constants</i>,
-<i>floating-point constants</i>, <i>complex constants</i>,
-and <i>string constants</i>. Rune, integer, floating-point,
-and complex constants are
-collectively called <i>numeric constants</i>.
-</p>
-
-<p>
-A constant value is represented by a
-<a href="#Rune_literals">rune</a>,
-<a href="#Integer_literals">integer</a>,
-<a href="#Floating-point_literals">floating-point</a>,
-<a href="#Imaginary_literals">imaginary</a>,
-or
-<a href="#String_literals">string</a> literal,
-an identifier denoting a constant,
-a <a href="#Constant_expressions">constant expression</a>,
-a <a href="#Conversions">conversion</a> with a result that is a constant, or
-the result value of some built-in functions such as
-<code>unsafe.Sizeof</code> applied to any value,
-<code>cap</code> or <code>len</code> applied to
-<a href="#Length_and_capacity">some expressions</a>,
-<code>real</code> and <code>imag</code> applied to a complex constant
-and <code>complex</code> applied to numeric constants.
-The boolean truth values are represented by the predeclared constants
-<code>true</code> and <code>false</code>. The predeclared identifier
-<a href="#Iota">iota</a> denotes an integer constant.
-</p>
-
-<p>
-In general, complex constants are a form of
-<a href="#Constant_expressions">constant expression</a>
-and are discussed in that section.
-</p>
-
-<p>
-Numeric constants represent exact values of arbitrary precision and do not overflow.
-Consequently, there are no constants denoting the IEEE-754 negative zero, infinity,
-and not-a-number values.
-</p>
-
-<p>
-Constants may be <a href="#Types">typed</a> or <i>untyped</i>.
-Literal constants, <code>true</code>, <code>false</code>, <code>iota</code>,
-and certain <a href="#Constant_expressions">constant expressions</a>
-containing only untyped constant operands are untyped.
-</p>
-
-<p>
-A constant may be given a type explicitly by a <a href="#Constant_declarations">constant declaration</a>
-or <a href="#Conversions">conversion</a>, or implicitly when used in a
-<a href="#Variable_declarations">variable declaration</a> or an
-<a href="#Assignments">assignment</a> or as an
-operand in an <a href="#Expressions">expression</a>.
-It is an error if the constant value
-cannot be <a href="#Representability">represented</a> as a value of the respective type.
-</p>
-
-<p>
-An untyped constant has a <i>default type</i> which is the type to which the
-constant is implicitly converted in contexts where a typed value is required,
-for instance, in a <a href="#Short_variable_declarations">short variable declaration</a>
-such as <code>i := 0</code> where there is no explicit type.
-The default type of an untyped constant is <code>bool</code>, <code>rune</code>,
-<code>int</code>, <code>float64</code>, <code>complex128</code> or <code>string</code>
-respectively, depending on whether it is a boolean, rune, integer, floating-point,
-complex, or string constant.
-</p>
-
-<p>
-Implementation restriction: Although numeric constants have arbitrary
-precision in the language, a compiler may implement them using an
-internal representation with limited precision. That said, every
-implementation must:
-</p>
-
-<ul>
- <li>Represent integer constants with at least 256 bits.</li>
-
- <li>Represent floating-point constants, including the parts of
- a complex constant, with a mantissa of at least 256 bits
- and a signed binary exponent of at least 16 bits.</li>
-
- <li>Give an error if unable to represent an integer constant
- precisely.</li>
-
- <li>Give an error if unable to represent a floating-point or
- complex constant due to overflow.</li>
-
- <li>Round to the nearest representable constant if unable to
- represent a floating-point or complex constant due to limits
- on precision.</li>
-</ul>
-
-<p>
-These requirements apply both to literal constants and to the result
-of evaluating <a href="#Constant_expressions">constant
-expressions</a>.
-</p>
-
-
-<h2 id="Variables">Variables</h2>
-
-<p>
-A variable is a storage location for holding a <i>value</i>.
-The set of permissible values is determined by the
-variable's <i><a href="#Types">type</a></i>.
-</p>
-
-<p>
-A <a href="#Variable_declarations">variable declaration</a>
-or, for function parameters and results, the signature
-of a <a href="#Function_declarations">function declaration</a>
-or <a href="#Function_literals">function literal</a> reserves
-storage for a named variable.
-
-Calling the built-in function <a href="#Allocation"><code>new</code></a>
-or taking the address of a <a href="#Composite_literals">composite literal</a>
-allocates storage for a variable at run time.
-Such an anonymous variable is referred to via a (possibly implicit)
-<a href="#Address_operators">pointer indirection</a>.
-</p>
-
-<p>
-<i>Structured</i> variables of <a href="#Array_types">array</a>, <a href="#Slice_types">slice</a>,
-and <a href="#Struct_types">struct</a> types have elements and fields that may
-be <a href="#Address_operators">addressed</a> individually. Each such element
-acts like a variable.
-</p>
-
-<p>
-The <i>static type</i> (or just <i>type</i>) of a variable is the
-type given in its declaration, the type provided in the
-<code>new</code> call or composite literal, or the type of
-an element of a structured variable.
-Variables of interface type also have a distinct <i>dynamic type</i>,
-which is the concrete type of the value assigned to the variable at run time
-(unless the value is the predeclared identifier <code>nil</code>,
-which has no type).
-The dynamic type may vary during execution but values stored in interface
-variables are always <a href="#Assignability">assignable</a>
-to the static type of the variable.
-</p>
-
-<pre>
-var x interface{} // x is nil and has static type interface{}
-var v *T // v has value nil, static type *T
-x = 42 // x has value 42 and dynamic type int
-x = v // x has value (*T)(nil) and dynamic type *T
-</pre>
-
-<p>
-A variable's value is retrieved by referring to the variable in an
-<a href="#Expressions">expression</a>; it is the most recent value
-<a href="#Assignments">assigned</a> to the variable.
-If a variable has not yet been assigned a value, its value is the
-<a href="#The_zero_value">zero value</a> for its type.
-</p>
-
-
-<h2 id="Types">Types</h2>
-
-<p>
-A type determines a set of values together with operations and methods specific
-to those values. A type may be denoted by a <i>type name</i>, if it has one,
-or specified using a <i>type literal</i>, which composes a type from existing types.
-</p>
-
-<pre class="ebnf">
-Type = TypeName | TypeLit | "(" Type ")" .
-TypeName = identifier | QualifiedIdent .
-TypeLit = ArrayType | StructType | PointerType | FunctionType | InterfaceType |
- SliceType | MapType | ChannelType .
-</pre>
-
-<p>
-The language <a href="#Predeclared_identifiers">predeclares</a> certain type names.
-Others are introduced with <a href="#Type_declarations">type declarations</a>.
-<i>Composite types</i>—array, struct, pointer, function,
-interface, slice, map, and channel types—may be constructed using
-type literals.
-</p>
-
-<p>
-Each type <code>T</code> has an <i>underlying type</i>: If <code>T</code>
-is one of the predeclared boolean, numeric, or string types, or a type literal,
-the corresponding underlying
-type is <code>T</code> itself. Otherwise, <code>T</code>'s underlying type
-is the underlying type of the type to which <code>T</code> refers in its
-<a href="#Type_declarations">type declaration</a>.
-</p>
-
-<pre>
-type (
- A1 = string
- A2 = A1
-)
-
-type (
- B1 string
- B2 B1
- B3 []B1
- B4 B3
-)
-</pre>
-
-<p>
-The underlying type of <code>string</code>, <code>A1</code>, <code>A2</code>, <code>B1</code>,
-and <code>B2</code> is <code>string</code>.
-The underlying type of <code>[]B1</code>, <code>B3</code>, and <code>B4</code> is <code>[]B1</code>.
-</p>
-
-<h3 id="Method_sets">Method sets</h3>
-<p>
-A type has a (possibly empty) <i>method set</i> associated with it.
-The method set of an <a href="#Interface_types">interface type</a> is its interface.
-The method set of any other type <code>T</code> consists of all
-<a href="#Method_declarations">methods</a> declared with receiver type <code>T</code>.
-The method set of the corresponding <a href="#Pointer_types">pointer type</a> <code>*T</code>
-is the set of all methods declared with receiver <code>*T</code> or <code>T</code>
-(that is, it also contains the method set of <code>T</code>).
-Further rules apply to structs containing embedded fields, as described
-in the section on <a href="#Struct_types">struct types</a>.
-Any other type has an empty method set.
-In a method set, each method must have a
-<a href="#Uniqueness_of_identifiers">unique</a>
-non-<a href="#Blank_identifier">blank</a> <a href="#MethodName">method name</a>.
-</p>
-
-<p>
-The method set of a type determines the interfaces that the
-type <a href="#Interface_types">implements</a>
-and the methods that can be <a href="#Calls">called</a>
-using a receiver of that type.
-</p>
-
-<h3 id="Boolean_types">Boolean types</h3>
-
-<p>
-A <i>boolean type</i> represents the set of Boolean truth values
-denoted by the predeclared constants <code>true</code>
-and <code>false</code>. The predeclared boolean type is <code>bool</code>;
-it is a <a href="#Type_definitions">defined type</a>.
-</p>
-
-<h3 id="Numeric_types">Numeric types</h3>
-
-<p>
-A <i>numeric type</i> represents sets of integer or floating-point values.
-The predeclared architecture-independent numeric types are:
-</p>
-
-<pre class="grammar">
-uint8 the set of all unsigned 8-bit integers (0 to 255)
-uint16 the set of all unsigned 16-bit integers (0 to 65535)
-uint32 the set of all unsigned 32-bit integers (0 to 4294967295)
-uint64 the set of all unsigned 64-bit integers (0 to 18446744073709551615)
-
-int8 the set of all signed 8-bit integers (-128 to 127)
-int16 the set of all signed 16-bit integers (-32768 to 32767)
-int32 the set of all signed 32-bit integers (-2147483648 to 2147483647)
-int64 the set of all signed 64-bit integers (-9223372036854775808 to 9223372036854775807)
-
-float32 the set of all IEEE-754 32-bit floating-point numbers
-float64 the set of all IEEE-754 64-bit floating-point numbers
-
-complex64 the set of all complex numbers with float32 real and imaginary parts
-complex128 the set of all complex numbers with float64 real and imaginary parts
-
-byte alias for uint8
-rune alias for int32
-</pre>
-
-<p>
-The value of an <i>n</i>-bit integer is <i>n</i> bits wide and represented using
-<a href="https://en.wikipedia.org/wiki/Two's_complement">two's complement arithmetic</a>.
-</p>
-
-<p>
-There is also a set of predeclared numeric types with implementation-specific sizes:
-</p>
-
-<pre class="grammar">
-uint either 32 or 64 bits
-int same size as uint
-uintptr an unsigned integer large enough to store the uninterpreted bits of a pointer value
-</pre>
-
-<p>
-To avoid portability issues all numeric types are <a href="#Type_definitions">defined
-types</a> and thus distinct except
-<code>byte</code>, which is an <a href="#Alias_declarations">alias</a> for <code>uint8</code>, and
-<code>rune</code>, which is an alias for <code>int32</code>.
-Explicit conversions
-are required when different numeric types are mixed in an expression
-or assignment. For instance, <code>int32</code> and <code>int</code>
-are not the same type even though they may have the same size on a
-particular architecture.
-
-
-<h3 id="String_types">String types</h3>
-
-<p>
-A <i>string type</i> represents the set of string values.
-A string value is a (possibly empty) sequence of bytes.
-The number of bytes is called the length of the string and is never negative.
-Strings are immutable: once created,
-it is impossible to change the contents of a string.
-The predeclared string type is <code>string</code>;
-it is a <a href="#Type_definitions">defined type</a>.
-</p>
-
-<p>
-The length of a string <code>s</code> can be discovered using
-the built-in function <a href="#Length_and_capacity"><code>len</code></a>.
-The length is a compile-time constant if the string is a constant.
-A string's bytes can be accessed by integer <a href="#Index_expressions">indices</a>
-0 through <code>len(s)-1</code>.
-It is illegal to take the address of such an element; if
-<code>s[i]</code> is the <code>i</code>'th byte of a
-string, <code>&s[i]</code> is invalid.
-</p>
-
-
-<h3 id="Array_types">Array types</h3>
-
-<p>
-An array is a numbered sequence of elements of a single
-type, called the element type.
-The number of elements is called the length of the array and is never negative.
-</p>
-
-<pre class="ebnf">
-ArrayType = "[" ArrayLength "]" ElementType .
-ArrayLength = Expression .
-ElementType = Type .
-</pre>
-
-<p>
-The length is part of the array's type; it must evaluate to a
-non-negative <a href="#Constants">constant</a>
-<a href="#Representability">representable</a> by a value
-of type <code>int</code>.
-The length of array <code>a</code> can be discovered
-using the built-in function <a href="#Length_and_capacity"><code>len</code></a>.
-The elements can be addressed by integer <a href="#Index_expressions">indices</a>
-0 through <code>len(a)-1</code>.
-Array types are always one-dimensional but may be composed to form
-multi-dimensional types.
-</p>
-
-<pre>
-[32]byte
-[2*N] struct { x, y int32 }
-[1000]*float64
-[3][5]int
-[2][2][2]float64 // same as [2]([2]([2]float64))
-</pre>
-
-<h3 id="Slice_types">Slice types</h3>
-
-<p>
-A slice is a descriptor for a contiguous segment of an <i>underlying array</i> and
-provides access to a numbered sequence of elements from that array.
-A slice type denotes the set of all slices of arrays of its element type.
-The number of elements is called the length of the slice and is never negative.
-The value of an uninitialized slice is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-SliceType = "[" "]" ElementType .
-</pre>
-
-<p>
-The length of a slice <code>s</code> can be discovered by the built-in function
-<a href="#Length_and_capacity"><code>len</code></a>; unlike with arrays it may change during
-execution. The elements can be addressed by integer <a href="#Index_expressions">indices</a>
-0 through <code>len(s)-1</code>. The slice index of a
-given element may be less than the index of the same element in the
-underlying array.
-</p>
-<p>
-A slice, once initialized, is always associated with an underlying
-array that holds its elements. A slice therefore shares storage
-with its array and with other slices of the same array; by contrast,
-distinct arrays always represent distinct storage.
-</p>
-<p>
-The array underlying a slice may extend past the end of the slice.
-The <i>capacity</i> is a measure of that extent: it is the sum of
-the length of the slice and the length of the array beyond the slice;
-a slice of length up to that capacity can be created by
-<a href="#Slice_expressions"><i>slicing</i></a> a new one from the original slice.
-The capacity of a slice <code>a</code> can be discovered using the
-built-in function <a href="#Length_and_capacity"><code>cap(a)</code></a>.
-</p>
-
-<p>
-A new, initialized slice value for a given element type <code>T</code> is
-made using the built-in function
-<a href="#Making_slices_maps_and_channels"><code>make</code></a>,
-which takes a slice type
-and parameters specifying the length and optionally the capacity.
-A slice created with <code>make</code> always allocates a new, hidden array
-to which the returned slice value refers. That is, executing
-</p>
-
-<pre>
-make([]T, length, capacity)
-</pre>
-
-<p>
-produces the same slice as allocating an array and <a href="#Slice_expressions">slicing</a>
-it, so these two expressions are equivalent:
-</p>
-
-<pre>
-make([]int, 50, 100)
-new([100]int)[0:50]
-</pre>
-
-<p>
-Like arrays, slices are always one-dimensional but may be composed to construct
-higher-dimensional objects.
-With arrays of arrays, the inner arrays are, by construction, always the same length;
-however with slices of slices (or arrays of slices), the inner lengths may vary dynamically.
-Moreover, the inner slices must be initialized individually.
-</p>
-
-<h3 id="Struct_types">Struct types</h3>
-
-<p>
-A struct is a sequence of named elements, called fields, each of which has a
-name and a type. Field names may be specified explicitly (IdentifierList) or
-implicitly (EmbeddedField).
-Within a struct, non-<a href="#Blank_identifier">blank</a> field names must
-be <a href="#Uniqueness_of_identifiers">unique</a>.
-</p>
-
-<pre class="ebnf">
-StructType = "struct" "{" { FieldDecl ";" } "}" .
-FieldDecl = (IdentifierList Type | EmbeddedField) [ Tag ] .
-EmbeddedField = [ "*" ] TypeName .
-Tag = string_lit .
-</pre>
-
-<pre>
-// An empty struct.
-struct {}
-
-// A struct with 6 fields.
-struct {
- x, y int
- u float32
- _ float32 // padding
- A *[]int
- F func()
-}
-</pre>
-
-<p>
-A field declared with a type but no explicit field name is called an <i>embedded field</i>.
-An embedded field must be specified as
-a type name <code>T</code> or as a pointer to a non-interface type name <code>*T</code>,
-and <code>T</code> itself may not be
-a pointer type. The unqualified type name acts as the field name.
-</p>
-
-<pre>
-// A struct with four embedded fields of types T1, *T2, P.T3 and *P.T4
-struct {
- T1 // field name is T1
- *T2 // field name is T2
- P.T3 // field name is T3
- *P.T4 // field name is T4
- x, y int // field names are x and y
-}
-</pre>
-
-<p>
-The following declaration is illegal because field names must be unique
-in a struct type:
-</p>
-
-<pre>
-struct {
- T // conflicts with embedded field *T and *P.T
- *T // conflicts with embedded field T and *P.T
- *P.T // conflicts with embedded field T and *T
-}
-</pre>
-
-<p>
-A field or <a href="#Method_declarations">method</a> <code>f</code> of an
-embedded field in a struct <code>x</code> is called <i>promoted</i> if
-<code>x.f</code> is a legal <a href="#Selectors">selector</a> that denotes
-that field or method <code>f</code>.
-</p>
-
-<p>
-Promoted fields act like ordinary fields
-of a struct except that they cannot be used as field names in
-<a href="#Composite_literals">composite literals</a> of the struct.
-</p>
-
-<p>
-Given a struct type <code>S</code> and a <a href="#Type_definitions">defined type</a>
-<code>T</code>, promoted methods are included in the method set of the struct as follows:
-</p>
-<ul>
- <li>
- If <code>S</code> contains an embedded field <code>T</code>,
- the <a href="#Method_sets">method sets</a> of <code>S</code>
- and <code>*S</code> both include promoted methods with receiver
- <code>T</code>. The method set of <code>*S</code> also
- includes promoted methods with receiver <code>*T</code>.
- </li>
-
- <li>
- If <code>S</code> contains an embedded field <code>*T</code>,
- the method sets of <code>S</code> and <code>*S</code> both
- include promoted methods with receiver <code>T</code> or
- <code>*T</code>.
- </li>
-</ul>
-
-<p>
-A field declaration may be followed by an optional string literal <i>tag</i>,
-which becomes an attribute for all the fields in the corresponding
-field declaration. An empty tag string is equivalent to an absent tag.
-The tags are made visible through a <a href="/pkg/reflect/#StructTag">reflection interface</a>
-and take part in <a href="#Type_identity">type identity</a> for structs
-but are otherwise ignored.
-</p>
-
-<pre>
-struct {
- x, y float64 "" // an empty tag string is like an absent tag
- name string "any string is permitted as a tag"
- _ [4]byte "ceci n'est pas un champ de structure"
-}
-
-// A struct corresponding to a TimeStamp protocol buffer.
-// The tag strings define the protocol buffer field numbers;
-// they follow the convention outlined by the reflect package.
-struct {
- microsec uint64 `protobuf:"1"`
- serverIP6 uint64 `protobuf:"2"`
-}
-</pre>
-
-<h3 id="Pointer_types">Pointer types</h3>
-
-<p>
-A pointer type denotes the set of all pointers to <a href="#Variables">variables</a> of a given
-type, called the <i>base type</i> of the pointer.
-The value of an uninitialized pointer is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-PointerType = "*" BaseType .
-BaseType = Type .
-</pre>
-
-<pre>
-*Point
-*[4]int
-</pre>
-
-<h3 id="Function_types">Function types</h3>
-
-<p>
-A function type denotes the set of all functions with the same parameter
-and result types. The value of an uninitialized variable of function type
-is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-FunctionType = "func" Signature .
-Signature = Parameters [ Result ] .
-Result = Parameters | Type .
-Parameters = "(" [ ParameterList [ "," ] ] ")" .
-ParameterList = ParameterDecl { "," ParameterDecl } .
-ParameterDecl = [ IdentifierList ] [ "..." ] Type .
-</pre>
-
-<p>
-Within a list of parameters or results, the names (IdentifierList)
-must either all be present or all be absent. If present, each name
-stands for one item (parameter or result) of the specified type and
-all non-<a href="#Blank_identifier">blank</a> names in the signature
-must be <a href="#Uniqueness_of_identifiers">unique</a>.
-If absent, each type stands for one item of that type.
-Parameter and result
-lists are always parenthesized except that if there is exactly
-one unnamed result it may be written as an unparenthesized type.
-</p>
-
-<p>
-The final incoming parameter in a function signature may have
-a type prefixed with <code>...</code>.
-A function with such a parameter is called <i>variadic</i> and
-may be invoked with zero or more arguments for that parameter.
-</p>
-
-<pre>
-func()
-func(x int) int
-func(a, _ int, z float32) bool
-func(a, b int, z float32) (bool)
-func(prefix string, values ...int)
-func(a, b int, z float64, opt ...interface{}) (success bool)
-func(int, int, float64) (float64, *[]int)
-func(n int) func(p *T)
-</pre>
-
-
-<h3 id="Interface_types">Interface types</h3>
-
-<p>
-An interface type specifies a <a href="#Method_sets">method set</a> called its <i>interface</i>.
-A variable of interface type can store a value of any type with a method set
-that is any superset of the interface. Such a type is said to
-<i>implement the interface</i>.
-The value of an uninitialized variable of interface type is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-InterfaceType = "interface" "{" { ( MethodSpec | InterfaceTypeName ) ";" } "}" .
-MethodSpec = MethodName Signature .
-MethodName = identifier .
-InterfaceTypeName = TypeName .
-</pre>
-
-<p>
-An interface type may specify methods <i>explicitly</i> through method specifications,
-or it may <i>embed</i> methods of other interfaces through interface type names.
-</p>
-
-<pre>
-// A simple File interface.
-interface {
- Read([]byte) (int, error)
- Write([]byte) (int, error)
- Close() error
-}
-</pre>
-
-<p>
-The name of each explicitly specified method must be <a href="#Uniqueness_of_identifiers">unique</a>
-and not <a href="#Blank_identifier">blank</a>.
-</p>
-
-<pre>
-interface {
- String() string
- String() string // illegal: String not unique
- _(x int) // illegal: method must have non-blank name
-}
-</pre>
-
-<p>
-More than one type may implement an interface.
-For instance, if two types <code>S1</code> and <code>S2</code>
-have the method set
-</p>
-
-<pre>
-func (p T) Read(p []byte) (n int, err error)
-func (p T) Write(p []byte) (n int, err error)
-func (p T) Close() error
-</pre>
-
-<p>
-(where <code>T</code> stands for either <code>S1</code> or <code>S2</code>)
-then the <code>File</code> interface is implemented by both <code>S1</code> and
-<code>S2</code>, regardless of what other methods
-<code>S1</code> and <code>S2</code> may have or share.
-</p>
-
-<p>
-A type implements any interface comprising any subset of its methods
-and may therefore implement several distinct interfaces. For
-instance, all types implement the <i>empty interface</i>:
-</p>
-
-<pre>
-interface{}
-</pre>
-
-<p>
-Similarly, consider this interface specification,
-which appears within a <a href="#Type_declarations">type declaration</a>
-to define an interface called <code>Locker</code>:
-</p>
-
-<pre>
-type Locker interface {
- Lock()
- Unlock()
-}
-</pre>
-
-<p>
-If <code>S1</code> and <code>S2</code> also implement
-</p>
-
-<pre>
-func (p T) Lock() { … }
-func (p T) Unlock() { … }
-</pre>
-
-<p>
-they implement the <code>Locker</code> interface as well
-as the <code>File</code> interface.
-</p>
-
-<p>
-An interface <code>T</code> may use a (possibly qualified) interface type
-name <code>E</code> in place of a method specification. This is called
-<i>embedding</i> interface <code>E</code> in <code>T</code>.
-The <a href="#Method_sets">method set</a> of <code>T</code> is the <i>union</i>
-of the method sets of <code>T</code>’s explicitly declared methods and of
-<code>T</code>’s embedded interfaces.
-</p>
-
-<pre>
-type Reader interface {
- Read(p []byte) (n int, err error)
- Close() error
-}
-
-type Writer interface {
- Write(p []byte) (n int, err error)
- Close() error
-}
-
-// ReadWriter's methods are Read, Write, and Close.
-type ReadWriter interface {
- Reader // includes methods of Reader in ReadWriter's method set
- Writer // includes methods of Writer in ReadWriter's method set
-}
-</pre>
-
-<p>
-A <i>union</i> of method sets contains the (exported and non-exported)
-methods of each method set exactly once, and methods with the
-<a href="#Uniqueness_of_identifiers">same</a> names must
-have <a href="#Type_identity">identical</a> signatures.
-</p>
-
-<pre>
-type ReadCloser interface {
- Reader // includes methods of Reader in ReadCloser's method set
- Close() // illegal: signatures of Reader.Close and Close are different
-}
-</pre>
-
-<p>
-An interface type <code>T</code> may not embed itself
-or any interface type that embeds <code>T</code>, recursively.
-</p>
-
-<pre>
-// illegal: Bad cannot embed itself
-type Bad interface {
- Bad
-}
-
-// illegal: Bad1 cannot embed itself using Bad2
-type Bad1 interface {
- Bad2
-}
-type Bad2 interface {
- Bad1
-}
-</pre>
-
-<h3 id="Map_types">Map types</h3>
-
-<p>
-A map is an unordered group of elements of one type, called the
-element type, indexed by a set of unique <i>keys</i> of another type,
-called the key type.
-The value of an uninitialized map is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-MapType = "map" "[" KeyType "]" ElementType .
-KeyType = Type .
-</pre>
-
-<p>
-The <a href="#Comparison_operators">comparison operators</a>
-<code>==</code> and <code>!=</code> must be fully defined
-for operands of the key type; thus the key type must not be a function, map, or
-slice.
-If the key type is an interface type, these
-comparison operators must be defined for the dynamic key values;
-failure will cause a <a href="#Run_time_panics">run-time panic</a>.
-
-</p>
-
-<pre>
-map[string]int
-map[*T]struct{ x, y float64 }
-map[string]interface{}
-</pre>
-
-<p>
-The number of map elements is called its length.
-For a map <code>m</code>, it can be discovered using the
-built-in function <a href="#Length_and_capacity"><code>len</code></a>
-and may change during execution. Elements may be added during execution
-using <a href="#Assignments">assignments</a> and retrieved with
-<a href="#Index_expressions">index expressions</a>; they may be removed with the
-<a href="#Deletion_of_map_elements"><code>delete</code></a> built-in function.
-</p>
-<p>
-A new, empty map value is made using the built-in
-function <a href="#Making_slices_maps_and_channels"><code>make</code></a>,
-which takes the map type and an optional capacity hint as arguments:
-</p>
-
-<pre>
-make(map[string]int)
-make(map[string]int, 100)
-</pre>
-
-<p>
-The initial capacity does not bound its size:
-maps grow to accommodate the number of items
-stored in them, with the exception of <code>nil</code> maps.
-A <code>nil</code> map is equivalent to an empty map except that no elements
-may be added.
-
-<h3 id="Channel_types">Channel types</h3>
-
-<p>
-A channel provides a mechanism for
-<a href="#Go_statements">concurrently executing functions</a>
-to communicate by
-<a href="#Send_statements">sending</a> and
-<a href="#Receive_operator">receiving</a>
-values of a specified element type.
-The value of an uninitialized channel is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-ChannelType = ( "chan" | "chan" "<-" | "<-" "chan" ) ElementType .
-</pre>
-
-<p>
-The optional <code><-</code> operator specifies the channel <i>direction</i>,
-<i>send</i> or <i>receive</i>. If no direction is given, the channel is
-<i>bidirectional</i>.
-A channel may be constrained only to send or only to receive by
-<a href="#Assignments">assignment</a> or
-explicit <a href="#Conversions">conversion</a>.
-</p>
-
-<pre>
-chan T // can be used to send and receive values of type T
-chan<- float64 // can only be used to send float64s
-<-chan int // can only be used to receive ints
-</pre>
-
-<p>
-The <code><-</code> operator associates with the leftmost <code>chan</code>
-possible:
-</p>
-
-<pre>
-chan<- chan int // same as chan<- (chan int)
-chan<- <-chan int // same as chan<- (<-chan int)
-<-chan <-chan int // same as <-chan (<-chan int)
-chan (<-chan int)
-</pre>
-
-<p>
-A new, initialized channel
-value can be made using the built-in function
-<a href="#Making_slices_maps_and_channels"><code>make</code></a>,
-which takes the channel type and an optional <i>capacity</i> as arguments:
-</p>
-
-<pre>
-make(chan int, 100)
-</pre>
-
-<p>
-The capacity, in number of elements, sets the size of the buffer in the channel.
-If the capacity is zero or absent, the channel is unbuffered and communication
-succeeds only when both a sender and receiver are ready. Otherwise, the channel
-is buffered and communication succeeds without blocking if the buffer
-is not full (sends) or not empty (receives).
-A <code>nil</code> channel is never ready for communication.
-</p>
-
-<p>
-A channel may be closed with the built-in function
-<a href="#Close"><code>close</code></a>.
-The multi-valued assignment form of the
-<a href="#Receive_operator">receive operator</a>
-reports whether a received value was sent before
-the channel was closed.
-</p>
-
-<p>
-A single channel may be used in
-<a href="#Send_statements">send statements</a>,
-<a href="#Receive_operator">receive operations</a>,
-and calls to the built-in functions
-<a href="#Length_and_capacity"><code>cap</code></a> and
-<a href="#Length_and_capacity"><code>len</code></a>
-by any number of goroutines without further synchronization.
-Channels act as first-in-first-out queues.
-For example, if one goroutine sends values on a channel
-and a second goroutine receives them, the values are
-received in the order sent.
-</p>
-
-<h2 id="Properties_of_types_and_values">Properties of types and values</h2>
-
-<h3 id="Type_identity">Type identity</h3>
-
-<p>
-Two types are either <i>identical</i> or <i>different</i>.
-</p>
-
-<p>
-A <a href="#Type_definitions">defined type</a> is always different from any other type.
-Otherwise, two types are identical if their <a href="#Types">underlying</a> type literals are
-structurally equivalent; that is, they have the same literal structure and corresponding
-components have identical types. In detail:
-</p>
-
-<ul>
- <li>Two array types are identical if they have identical element types and
- the same array length.</li>
-
- <li>Two slice types are identical if they have identical element types.</li>
-
- <li>Two struct types are identical if they have the same sequence of fields,
- and if corresponding fields have the same names, and identical types,
- and identical tags.
- <a href="#Exported_identifiers">Non-exported</a> field names from different
- packages are always different.</li>
-
- <li>Two pointer types are identical if they have identical base types.</li>
-
- <li>Two function types are identical if they have the same number of parameters
- and result values, corresponding parameter and result types are
- identical, and either both functions are variadic or neither is.
- Parameter and result names are not required to match.</li>
-
- <li>Two interface types are identical if they have the same set of methods
- with the same names and identical function types.
- <a href="#Exported_identifiers">Non-exported</a> method names from different
- packages are always different. The order of the methods is irrelevant.</li>
-
- <li>Two map types are identical if they have identical key and element types.</li>
-
- <li>Two channel types are identical if they have identical element types and
- the same direction.</li>
-</ul>
-
-<p>
-Given the declarations
-</p>
-
-<pre>
-type (
- A0 = []string
- A1 = A0
- A2 = struct{ a, b int }
- A3 = int
- A4 = func(A3, float64) *A0
- A5 = func(x int, _ float64) *[]string
-)
-
-type (
- B0 A0
- B1 []string
- B2 struct{ a, b int }
- B3 struct{ a, c int }
- B4 func(int, float64) *B0
- B5 func(x int, y float64) *A1
-)
-
-type C0 = B0
-</pre>
-
-<p>
-these types are identical:
-</p>
-
-<pre>
-A0, A1, and []string
-A2 and struct{ a, b int }
-A3 and int
-A4, func(int, float64) *[]string, and A5
-
-B0 and C0
-[]int and []int
-struct{ a, b *T5 } and struct{ a, b *T5 }
-func(x int, y float64) *[]string, func(int, float64) (result *[]string), and A5
-</pre>
-
-<p>
-<code>B0</code> and <code>B1</code> are different because they are new types
-created by distinct <a href="#Type_definitions">type definitions</a>;
-<code>func(int, float64) *B0</code> and <code>func(x int, y float64) *[]string</code>
-are different because <code>B0</code> is different from <code>[]string</code>.
-</p>
-
-
-<h3 id="Assignability">Assignability</h3>
-
-<p>
-A value <code>x</code> is <i>assignable</i> to a <a href="#Variables">variable</a> of type <code>T</code>
-("<code>x</code> is assignable to <code>T</code>") if one of the following conditions applies:
-</p>
-
-<ul>
-<li>
-<code>x</code>'s type is identical to <code>T</code>.
-</li>
-<li>
-<code>x</code>'s type <code>V</code> and <code>T</code> have identical
-<a href="#Types">underlying types</a> and at least one of <code>V</code>
-or <code>T</code> is not a <a href="#Type_definitions">defined</a> type.
-</li>
-<li>
-<code>T</code> is an interface type and
-<code>x</code> <a href="#Interface_types">implements</a> <code>T</code>.
-</li>
-<li>
-<code>x</code> is a bidirectional channel value, <code>T</code> is a channel type,
-<code>x</code>'s type <code>V</code> and <code>T</code> have identical element types,
-and at least one of <code>V</code> or <code>T</code> is not a defined type.
-</li>
-<li>
-<code>x</code> is the predeclared identifier <code>nil</code> and <code>T</code>
-is a pointer, function, slice, map, channel, or interface type.
-</li>
-<li>
-<code>x</code> is an untyped <a href="#Constants">constant</a>
-<a href="#Representability">representable</a>
-by a value of type <code>T</code>.
-</li>
-</ul>
-
-
-<h3 id="Representability">Representability</h3>
-
-<p>
-A <a href="#Constants">constant</a> <code>x</code> is <i>representable</i>
-by a value of type <code>T</code> if one of the following conditions applies:
-</p>
-
-<ul>
-<li>
-<code>x</code> is in the set of values <a href="#Types">determined</a> by <code>T</code>.
-</li>
-
-<li>
-<code>T</code> is a floating-point type and <code>x</code> can be rounded to <code>T</code>'s
-precision without overflow. Rounding uses IEEE 754 round-to-even rules but with an IEEE
-negative zero further simplified to an unsigned zero. Note that constant values never result
-in an IEEE negative zero, NaN, or infinity.
-</li>
-
-<li>
-<code>T</code> is a complex type, and <code>x</code>'s
-<a href="#Complex_numbers">components</a> <code>real(x)</code> and <code>imag(x)</code>
-are representable by values of <code>T</code>'s component type (<code>float32</code> or
-<code>float64</code>).
-</li>
-</ul>
-
-<pre>
-x T x is representable by a value of T because
-
-'a' byte 97 is in the set of byte values
-97 rune rune is an alias for int32, and 97 is in the set of 32-bit integers
-"foo" string "foo" is in the set of string values
-1024 int16 1024 is in the set of 16-bit integers
-42.0 byte 42 is in the set of unsigned 8-bit integers
-1e10 uint64 10000000000 is in the set of unsigned 64-bit integers
-2.718281828459045 float32 2.718281828459045 rounds to 2.7182817 which is in the set of float32 values
--1e-1000 float64 -1e-1000 rounds to IEEE -0.0 which is further simplified to 0.0
-0i int 0 is an integer value
-(42 + 0i) float32 42.0 (with zero imaginary part) is in the set of float32 values
-</pre>
-
-<pre>
-x T x is not representable by a value of T because
-
-0 bool 0 is not in the set of boolean values
-'a' string 'a' is a rune, it is not in the set of string values
-1024 byte 1024 is not in the set of unsigned 8-bit integers
--1 uint16 -1 is not in the set of unsigned 16-bit integers
-1.1 int 1.1 is not an integer value
-42i float32 (0 + 42i) is not in the set of float32 values
-1e1000 float64 1e1000 overflows to IEEE +Inf after rounding
-</pre>
-
-
-<h2 id="Blocks">Blocks</h2>
-
-<p>
-A <i>block</i> is a possibly empty sequence of declarations and statements
-within matching brace brackets.
-</p>
-
-<pre class="ebnf">
-Block = "{" StatementList "}" .
-StatementList = { Statement ";" } .
-</pre>
-
-<p>
-In addition to explicit blocks in the source code, there are implicit blocks:
-</p>
-
-<ol>
- <li>The <i>universe block</i> encompasses all Go source text.</li>
-
- <li>Each <a href="#Packages">package</a> has a <i>package block</i> containing all
- Go source text for that package.</li>
-
- <li>Each file has a <i>file block</i> containing all Go source text
- in that file.</li>
-
- <li>Each <a href="#If_statements">"if"</a>,
- <a href="#For_statements">"for"</a>, and
- <a href="#Switch_statements">"switch"</a>
- statement is considered to be in its own implicit block.</li>
-
- <li>Each clause in a <a href="#Switch_statements">"switch"</a>
- or <a href="#Select_statements">"select"</a> statement
- acts as an implicit block.</li>
-</ol>
-
-<p>
-Blocks nest and influence <a href="#Declarations_and_scope">scoping</a>.
-</p>
-
-
-<h2 id="Declarations_and_scope">Declarations and scope</h2>
-
-<p>
-A <i>declaration</i> binds a non-<a href="#Blank_identifier">blank</a> identifier to a
-<a href="#Constant_declarations">constant</a>,
-<a href="#Type_declarations">type</a>,
-<a href="#Variable_declarations">variable</a>,
-<a href="#Function_declarations">function</a>,
-<a href="#Labeled_statements">label</a>, or
-<a href="#Import_declarations">package</a>.
-Every identifier in a program must be declared.
-No identifier may be declared twice in the same block, and
-no identifier may be declared in both the file and package block.
-</p>
-
-<p>
-The <a href="#Blank_identifier">blank identifier</a> may be used like any other identifier
-in a declaration, but it does not introduce a binding and thus is not declared.
-In the package block, the identifier <code>init</code> may only be used for
-<a href="#Package_initialization"><code>init</code> function</a> declarations,
-and like the blank identifier it does not introduce a new binding.
-</p>
-
-<pre class="ebnf">
-Declaration = ConstDecl | TypeDecl | VarDecl .
-TopLevelDecl = Declaration | FunctionDecl | MethodDecl .
-</pre>
-
-<p>
-The <i>scope</i> of a declared identifier is the extent of source text in which
-the identifier denotes the specified constant, type, variable, function, label, or package.
-</p>
-
-<p>
-Go is lexically scoped using <a href="#Blocks">blocks</a>:
-</p>
-
-<ol>
- <li>The scope of a <a href="#Predeclared_identifiers">predeclared identifier</a> is the universe block.</li>
-
- <li>The scope of an identifier denoting a constant, type, variable,
- or function (but not method) declared at top level (outside any
- function) is the package block.</li>
-
- <li>The scope of the package name of an imported package is the file block
- of the file containing the import declaration.</li>
-
- <li>The scope of an identifier denoting a method receiver, function parameter,
- or result variable is the function body.</li>
-
- <li>The scope of a constant or variable identifier declared
- inside a function begins at the end of the ConstSpec or VarSpec
- (ShortVarDecl for short variable declarations)
- and ends at the end of the innermost containing block.</li>
-
- <li>The scope of a type identifier declared inside a function
- begins at the identifier in the TypeSpec
- and ends at the end of the innermost containing block.</li>
-</ol>
-
-<p>
-An identifier declared in a block may be redeclared in an inner block.
-While the identifier of the inner declaration is in scope, it denotes
-the entity declared by the inner declaration.
-</p>
-
-<p>
-The <a href="#Package_clause">package clause</a> is not a declaration; the package name
-does not appear in any scope. Its purpose is to identify the files belonging
-to the same <a href="#Packages">package</a> and to specify the default package name for import
-declarations.
-</p>
-
-
-<h3 id="Label_scopes">Label scopes</h3>
-
-<p>
-Labels are declared by <a href="#Labeled_statements">labeled statements</a> and are
-used in the <a href="#Break_statements">"break"</a>,
-<a href="#Continue_statements">"continue"</a>, and
-<a href="#Goto_statements">"goto"</a> statements.
-It is illegal to define a label that is never used.
-In contrast to other identifiers, labels are not block scoped and do
-not conflict with identifiers that are not labels. The scope of a label
-is the body of the function in which it is declared and excludes
-the body of any nested function.
-</p>
-
-
-<h3 id="Blank_identifier">Blank identifier</h3>
-
-<p>
-The <i>blank identifier</i> is represented by the underscore character <code>_</code>.
-It serves as an anonymous placeholder instead of a regular (non-blank)
-identifier and has special meaning in <a href="#Declarations_and_scope">declarations</a>,
-as an <a href="#Operands">operand</a>, and in <a href="#Assignments">assignments</a>.
-</p>
-
-
-<h3 id="Predeclared_identifiers">Predeclared identifiers</h3>
-
-<p>
-The following identifiers are implicitly declared in the
-<a href="#Blocks">universe block</a>:
-</p>
-<pre class="grammar">
-Types:
- bool byte complex64 complex128 error float32 float64
- int int8 int16 int32 int64 rune string
- uint uint8 uint16 uint32 uint64 uintptr
-
-Constants:
- true false iota
-
-Zero value:
- nil
-
-Functions:
- append cap close complex copy delete imag len
- make new panic print println real recover
-</pre>
-
-
-<h3 id="Exported_identifiers">Exported identifiers</h3>
-
-<p>
-An identifier may be <i>exported</i> to permit access to it from another package.
-An identifier is exported if both:
-</p>
-<ol>
- <li>the first character of the identifier's name is a Unicode upper case
- letter (Unicode class "Lu"); and</li>
- <li>the identifier is declared in the <a href="#Blocks">package block</a>
- or it is a <a href="#Struct_types">field name</a> or
- <a href="#MethodName">method name</a>.</li>
-</ol>
-<p>
-All other identifiers are not exported.
-</p>
-
-
-<h3 id="Uniqueness_of_identifiers">Uniqueness of identifiers</h3>
-
-<p>
-Given a set of identifiers, an identifier is called <i>unique</i> if it is
-<i>different</i> from every other in the set.
-Two identifiers are different if they are spelled differently, or if they
-appear in different <a href="#Packages">packages</a> and are not
-<a href="#Exported_identifiers">exported</a>. Otherwise, they are the same.
-</p>
-
-<h3 id="Constant_declarations">Constant declarations</h3>
-
-<p>
-A constant declaration binds a list of identifiers (the names of
-the constants) to the values of a list of <a href="#Constant_expressions">constant expressions</a>.
-The number of identifiers must be equal
-to the number of expressions, and the <i>n</i>th identifier on
-the left is bound to the value of the <i>n</i>th expression on the
-right.
-</p>
-
-<pre class="ebnf">
-ConstDecl = "const" ( ConstSpec | "(" { ConstSpec ";" } ")" ) .
-ConstSpec = IdentifierList [ [ Type ] "=" ExpressionList ] .
-
-IdentifierList = identifier { "," identifier } .
-ExpressionList = Expression { "," Expression } .
-</pre>
-
-<p>
-If the type is present, all constants take the type specified, and
-the expressions must be <a href="#Assignability">assignable</a> to that type.
-If the type is omitted, the constants take the
-individual types of the corresponding expressions.
-If the expression values are untyped <a href="#Constants">constants</a>,
-the declared constants remain untyped and the constant identifiers
-denote the constant values. For instance, if the expression is a
-floating-point literal, the constant identifier denotes a floating-point
-constant, even if the literal's fractional part is zero.
-</p>
-
-<pre>
-const Pi float64 = 3.14159265358979323846
-const zero = 0.0 // untyped floating-point constant
-const (
- size int64 = 1024
- eof = -1 // untyped integer constant
-)
-const a, b, c = 3, 4, "foo" // a = 3, b = 4, c = "foo", untyped integer and string constants
-const u, v float32 = 0, 3 // u = 0.0, v = 3.0
-</pre>
-
-<p>
-Within a parenthesized <code>const</code> declaration list the
-expression list may be omitted from any but the first ConstSpec.
-Such an empty list is equivalent to the textual substitution of the
-first preceding non-empty expression list and its type if any.
-Omitting the list of expressions is therefore equivalent to
-repeating the previous list. The number of identifiers must be equal
-to the number of expressions in the previous list.
-Together with the <a href="#Iota"><code>iota</code> constant generator</a>
-this mechanism permits light-weight declaration of sequential values:
-</p>
-
-<pre>
-const (
- Sunday = iota
- Monday
- Tuesday
- Wednesday
- Thursday
- Friday
- Partyday
- numberOfDays // this constant is not exported
-)
-</pre>
-
-
-<h3 id="Iota">Iota</h3>
-
-<p>
-Within a <a href="#Constant_declarations">constant declaration</a>, the predeclared identifier
-<code>iota</code> represents successive untyped integer <a href="#Constants">
-constants</a>. Its value is the index of the respective <a href="#ConstSpec">ConstSpec</a>
-in that constant declaration, starting at zero.
-It can be used to construct a set of related constants:
-</p>
-
-<pre>
-const (
- c0 = iota // c0 == 0
- c1 = iota // c1 == 1
- c2 = iota // c2 == 2
-)
-
-const (
- a = 1 << iota // a == 1 (iota == 0)
- b = 1 << iota // b == 2 (iota == 1)
- c = 3 // c == 3 (iota == 2, unused)
- d = 1 << iota // d == 8 (iota == 3)
-)
-
-const (
- u = iota * 42 // u == 0 (untyped integer constant)
- v float64 = iota * 42 // v == 42.0 (float64 constant)
- w = iota * 42 // w == 84 (untyped integer constant)
-)
-
-const x = iota // x == 0
-const y = iota // y == 0
-</pre>
-
-<p>
-By definition, multiple uses of <code>iota</code> in the same ConstSpec all have the same value:
-</p>
-
-<pre>
-const (
- bit0, mask0 = 1 << iota, 1<<iota - 1 // bit0 == 1, mask0 == 0 (iota == 0)
- bit1, mask1 // bit1 == 2, mask1 == 1 (iota == 1)
- _, _ // (iota == 2, unused)
- bit3, mask3 // bit3 == 8, mask3 == 7 (iota == 3)
-)
-</pre>
-
-<p>
-This last example exploits the <a href="#Constant_declarations">implicit repetition</a>
-of the last non-empty expression list.
-</p>
-
-
-<h3 id="Type_declarations">Type declarations</h3>
-
-<p>
-A type declaration binds an identifier, the <i>type name</i>, to a <a href="#Types">type</a>.
-Type declarations come in two forms: alias declarations and type definitions.
-</p>
-
-<pre class="ebnf">
-TypeDecl = "type" ( TypeSpec | "(" { TypeSpec ";" } ")" ) .
-TypeSpec = AliasDecl | TypeDef .
-</pre>
-
-<h4 id="Alias_declarations">Alias declarations</h4>
-
-<p>
-An alias declaration binds an identifier to the given type.
-</p>
-
-<pre class="ebnf">
-AliasDecl = identifier "=" Type .
-</pre>
-
-<p>
-Within the <a href="#Declarations_and_scope">scope</a> of
-the identifier, it serves as an <i>alias</i> for the type.
-</p>
-
-<pre>
-type (
- nodeList = []*Node // nodeList and []*Node are identical types
- Polar = polar // Polar and polar denote identical types
-)
-</pre>
-
-
-<h4 id="Type_definitions">Type definitions</h4>
-
-<p>
-A type definition creates a new, distinct type with the same
-<a href="#Types">underlying type</a> and operations as the given type,
-and binds an identifier to it.
-</p>
-
-<pre class="ebnf">
-TypeDef = identifier Type .
-</pre>
-
-<p>
-The new type is called a <i>defined type</i>.
-It is <a href="#Type_identity">different</a> from any other type,
-including the type it is created from.
-</p>
-
-<pre>
-type (
- Point struct{ x, y float64 } // Point and struct{ x, y float64 } are different types
- polar Point // polar and Point denote different types
-)
-
-type TreeNode struct {
- left, right *TreeNode
- value *Comparable
-}
-
-type Block interface {
- BlockSize() int
- Encrypt(src, dst []byte)
- Decrypt(src, dst []byte)
-}
-</pre>
-
-<p>
-A defined type may have <a href="#Method_declarations">methods</a> associated with it.
-It does not inherit any methods bound to the given type,
-but the <a href="#Method_sets">method set</a>
-of an interface type or of elements of a composite type remains unchanged:
-</p>
-
-<pre>
-// A Mutex is a data type with two methods, Lock and Unlock.
-type Mutex struct { /* Mutex fields */ }
-func (m *Mutex) Lock() { /* Lock implementation */ }
-func (m *Mutex) Unlock() { /* Unlock implementation */ }
-
-// NewMutex has the same composition as Mutex but its method set is empty.
-type NewMutex Mutex
-
-// The method set of PtrMutex's underlying type *Mutex remains unchanged,
-// but the method set of PtrMutex is empty.
-type PtrMutex *Mutex
-
-// The method set of *PrintableMutex contains the methods
-// Lock and Unlock bound to its embedded field Mutex.
-type PrintableMutex struct {
- Mutex
-}
-
-// MyBlock is an interface type that has the same method set as Block.
-type MyBlock Block
-</pre>
-
-<p>
-Type definitions may be used to define different boolean, numeric,
-or string types and associate methods with them:
-</p>
-
-<pre>
-type TimeZone int
-
-const (
- EST TimeZone = -(5 + iota)
- CST
- MST
- PST
-)
-
-func (tz TimeZone) String() string {
- return fmt.Sprintf("GMT%+dh", tz)
-}
-</pre>
-
-
-<h3 id="Variable_declarations">Variable declarations</h3>
-
-<p>
-A variable declaration creates one or more <a href="#Variables">variables</a>,
-binds corresponding identifiers to them, and gives each a type and an initial value.
-</p>
-
-<pre class="ebnf">
-VarDecl = "var" ( VarSpec | "(" { VarSpec ";" } ")" ) .
-VarSpec = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList ) .
-</pre>
-
-<pre>
-var i int
-var U, V, W float64
-var k = 0
-var x, y float32 = -1, -2
-var (
- i int
- u, v, s = 2.0, 3.0, "bar"
-)
-var re, im = complexSqrt(-1)
-var _, found = entries[name] // map lookup; only interested in "found"
-</pre>
-
-<p>
-If a list of expressions is given, the variables are initialized
-with the expressions following the rules for <a href="#Assignments">assignments</a>.
-Otherwise, each variable is initialized to its <a href="#The_zero_value">zero value</a>.
-</p>
-
-<p>
-If a type is present, each variable is given that type.
-Otherwise, each variable is given the type of the corresponding
-initialization value in the assignment.
-If that value is an untyped constant, it is first implicitly
-<a href="#Conversions">converted</a> to its <a href="#Constants">default type</a>;
-if it is an untyped boolean value, it is first implicitly converted to type <code>bool</code>.
-The predeclared value <code>nil</code> cannot be used to initialize a variable
-with no explicit type.
-</p>
-
-<pre>
-var d = math.Sin(0.5) // d is float64
-var i = 42 // i is int
-var t, ok = x.(T) // t is T, ok is bool
-var n = nil // illegal
-</pre>
-
-<p>
-Implementation restriction: A compiler may make it illegal to declare a variable
-inside a <a href="#Function_declarations">function body</a> if the variable is
-never used.
-</p>
-
-<h3 id="Short_variable_declarations">Short variable declarations</h3>
-
-<p>
-A <i>short variable declaration</i> uses the syntax:
-</p>
-
-<pre class="ebnf">
-ShortVarDecl = IdentifierList ":=" ExpressionList .
-</pre>
-
-<p>
-It is shorthand for a regular <a href="#Variable_declarations">variable declaration</a>
-with initializer expressions but no types:
-</p>
-
-<pre class="grammar">
-"var" IdentifierList = ExpressionList .
-</pre>
-
-<pre>
-i, j := 0, 10
-f := func() int { return 7 }
-ch := make(chan int)
-r, w, _ := os.Pipe() // os.Pipe() returns a connected pair of Files and an error, if any
-_, y, _ := coord(p) // coord() returns three values; only interested in y coordinate
-</pre>
-
-<p>
-Unlike regular variable declarations, a short variable declaration may <i>redeclare</i>
-variables provided they were originally declared earlier in the same block
-(or the parameter lists if the block is the function body) with the same type,
-and at least one of the non-<a href="#Blank_identifier">blank</a> variables is new.
-As a consequence, redeclaration can only appear in a multi-variable short declaration.
-Redeclaration does not introduce a new variable; it just assigns a new value to the original.
-</p>
-
-<pre>
-field1, offset := nextField(str, 0)
-field2, offset := nextField(str, offset) // redeclares offset
-a, a := 1, 2 // illegal: double declaration of a or no new variable if a was declared elsewhere
-</pre>
-
-<p>
-Short variable declarations may appear only inside functions.
-In some contexts such as the initializers for
-<a href="#If_statements">"if"</a>,
-<a href="#For_statements">"for"</a>, or
-<a href="#Switch_statements">"switch"</a> statements,
-they can be used to declare local temporary variables.
-</p>
-
-<h3 id="Function_declarations">Function declarations</h3>
-
-<p>
-A function declaration binds an identifier, the <i>function name</i>,
-to a function.
-</p>
-
-<pre class="ebnf">
-FunctionDecl = "func" FunctionName Signature [ FunctionBody ] .
-FunctionName = identifier .
-FunctionBody = Block .
-</pre>
-
-<p>
-If the function's <a href="#Function_types">signature</a> declares
-result parameters, the function body's statement list must end in
-a <a href="#Terminating_statements">terminating statement</a>.
-</p>
-
-<pre>
-func IndexRune(s string, r rune) int {
- for i, c := range s {
- if c == r {
- return i
- }
- }
- // invalid: missing return statement
-}
-</pre>
-
-<p>
-A function declaration may omit the body. Such a declaration provides the
-signature for a function implemented outside Go, such as an assembly routine.
-</p>
-
-<pre>
-func min(x int, y int) int {
- if x < y {
- return x
- }
- return y
-}
-
-func flushICache(begin, end uintptr) // implemented externally
-</pre>
-
-<h3 id="Method_declarations">Method declarations</h3>
-
-<p>
-A method is a <a href="#Function_declarations">function</a> with a <i>receiver</i>.
-A method declaration binds an identifier, the <i>method name</i>, to a method,
-and associates the method with the receiver's <i>base type</i>.
-</p>
-
-<pre class="ebnf">
-MethodDecl = "func" Receiver MethodName Signature [ FunctionBody ] .
-Receiver = Parameters .
-</pre>
-
-<p>
-The receiver is specified via an extra parameter section preceding the method
-name. That parameter section must declare a single non-variadic parameter, the receiver.
-Its type must be a <a href="#Type_definitions">defined</a> type <code>T</code> or a
-pointer to a defined type <code>T</code>. <code>T</code> is called the receiver
-<i>base type</i>. A receiver base type cannot be a pointer or interface type and
-it must be defined in the same package as the method.
-The method is said to be <i>bound</i> to its receiver base type and the method name
-is visible only within <a href="#Selectors">selectors</a> for type <code>T</code>
-or <code>*T</code>.
-</p>
-
-<p>
-A non-<a href="#Blank_identifier">blank</a> receiver identifier must be
-<a href="#Uniqueness_of_identifiers">unique</a> in the method signature.
-If the receiver's value is not referenced inside the body of the method,
-its identifier may be omitted in the declaration. The same applies in
-general to parameters of functions and methods.
-</p>
-
-<p>
-For a base type, the non-blank names of methods bound to it must be unique.
-If the base type is a <a href="#Struct_types">struct type</a>,
-the non-blank method and field names must be distinct.
-</p>
-
-<p>
-Given defined type <code>Point</code>, the declarations
-</p>
-
-<pre>
-func (p *Point) Length() float64 {
- return math.Sqrt(p.x * p.x + p.y * p.y)
-}
-
-func (p *Point) Scale(factor float64) {
- p.x *= factor
- p.y *= factor
-}
-</pre>
-
-<p>
-bind the methods <code>Length</code> and <code>Scale</code>,
-with receiver type <code>*Point</code>,
-to the base type <code>Point</code>.
-</p>
-
-<p>
-The type of a method is the type of a function with the receiver as first
-argument. For instance, the method <code>Scale</code> has type
-</p>
-
-<pre>
-func(p *Point, factor float64)
-</pre>
-
-<p>
-However, a function declared this way is not a method.
-</p>
-
-
-<h2 id="Expressions">Expressions</h2>
-
-<p>
-An expression specifies the computation of a value by applying
-operators and functions to operands.
-</p>
-
-<h3 id="Operands">Operands</h3>
-
-<p>
-Operands denote the elementary values in an expression. An operand may be a
-literal, a (possibly <a href="#Qualified_identifiers">qualified</a>)
-non-<a href="#Blank_identifier">blank</a> identifier denoting a
-<a href="#Constant_declarations">constant</a>,
-<a href="#Variable_declarations">variable</a>, or
-<a href="#Function_declarations">function</a>,
-or a parenthesized expression.
-</p>
-
-<p>
-The <a href="#Blank_identifier">blank identifier</a> may appear as an
-operand only on the left-hand side of an <a href="#Assignments">assignment</a>.
-</p>
-
-<pre class="ebnf">
-Operand = Literal | OperandName | "(" Expression ")" .
-Literal = BasicLit | CompositeLit | FunctionLit .
-BasicLit = int_lit | float_lit | imaginary_lit | rune_lit | string_lit .
-OperandName = identifier | QualifiedIdent .
-</pre>
-
-<h3 id="Qualified_identifiers">Qualified identifiers</h3>
-
-<p>
-A qualified identifier is an identifier qualified with a package name prefix.
-Both the package name and the identifier must not be
-<a href="#Blank_identifier">blank</a>.
-</p>
-
-<pre class="ebnf">
-QualifiedIdent = PackageName "." identifier .
-</pre>
-
-<p>
-A qualified identifier accesses an identifier in a different package, which
-must be <a href="#Import_declarations">imported</a>.
-The identifier must be <a href="#Exported_identifiers">exported</a> and
-declared in the <a href="#Blocks">package block</a> of that package.
-</p>
-
-<pre>
-math.Sin // denotes the Sin function in package math
-</pre>
-
-<h3 id="Composite_literals">Composite literals</h3>
-
-<p>
-Composite literals construct values for structs, arrays, slices, and maps
-and create a new value each time they are evaluated.
-They consist of the type of the literal followed by a brace-bound list of elements.
-Each element may optionally be preceded by a corresponding key.
-</p>
-
-<pre class="ebnf">
-CompositeLit = LiteralType LiteralValue .
-LiteralType = StructType | ArrayType | "[" "..." "]" ElementType |
- SliceType | MapType | TypeName .
-LiteralValue = "{" [ ElementList [ "," ] ] "}" .
-ElementList = KeyedElement { "," KeyedElement } .
-KeyedElement = [ Key ":" ] Element .
-Key = FieldName | Expression | LiteralValue .
-FieldName = identifier .
-Element = Expression | LiteralValue .
-</pre>
-
-<p>
-The LiteralType's underlying type must be a struct, array, slice, or map type
-(the grammar enforces this constraint except when the type is given
-as a TypeName).
-The types of the elements and keys must be <a href="#Assignability">assignable</a>
-to the respective field, element, and key types of the literal type;
-there is no additional conversion.
-The key is interpreted as a field name for struct literals,
-an index for array and slice literals, and a key for map literals.
-For map literals, all elements must have a key. It is an error
-to specify multiple elements with the same field name or
-constant key value. For non-constant map keys, see the section on
-<a href="#Order_of_evaluation">evaluation order</a>.
-</p>
-
-<p>
-For struct literals the following rules apply:
-</p>
-<ul>
- <li>A key must be a field name declared in the struct type.
- </li>
- <li>An element list that does not contain any keys must
- list an element for each struct field in the
- order in which the fields are declared.
- </li>
- <li>If any element has a key, every element must have a key.
- </li>
- <li>An element list that contains keys does not need to
- have an element for each struct field. Omitted fields
- get the zero value for that field.
- </li>
- <li>A literal may omit the element list; such a literal evaluates
- to the zero value for its type.
- </li>
- <li>It is an error to specify an element for a non-exported
- field of a struct belonging to a different package.
- </li>
-</ul>
-
-<p>
-Given the declarations
-</p>
-<pre>
-type Point3D struct { x, y, z float64 }
-type Line struct { p, q Point3D }
-</pre>
-
-<p>
-one may write
-</p>
-
-<pre>
-origin := Point3D{} // zero value for Point3D
-line := Line{origin, Point3D{y: -4, z: 12.3}} // zero value for line.q.x
-</pre>
-
-<p>
-For array and slice literals the following rules apply:
-</p>
-<ul>
- <li>Each element has an associated integer index marking
- its position in the array.
- </li>
- <li>An element with a key uses the key as its index. The
- key must be a non-negative constant
- <a href="#Representability">representable</a> by
- a value of type <code>int</code>; and if it is typed
- it must be of integer type.
- </li>
- <li>An element without a key uses the previous element's index plus one.
- If the first element has no key, its index is zero.
- </li>
-</ul>
-
-<p>
-<a href="#Address_operators">Taking the address</a> of a composite literal
-generates a pointer to a unique <a href="#Variables">variable</a> initialized
-with the literal's value.
-</p>
-
-<pre>
-var pointer *Point3D = &Point3D{y: 1000}
-</pre>
-
-<p>
-Note that the <a href="#The_zero_value">zero value</a> for a slice or map
-type is not the same as an initialized but empty value of the same type.
-Consequently, taking the address of an empty slice or map composite literal
-does not have the same effect as allocating a new slice or map value with
-<a href="#Allocation">new</a>.
-</p>
-
-<pre>
-p1 := &[]int{} // p1 points to an initialized, empty slice with value []int{} and length 0
-p2 := new([]int) // p2 points to an uninitialized slice with value nil and length 0
-</pre>
-
-<p>
-The length of an array literal is the length specified in the literal type.
-If fewer elements than the length are provided in the literal, the missing
-elements are set to the zero value for the array element type.
-It is an error to provide elements with index values outside the index range
-of the array. The notation <code>...</code> specifies an array length equal
-to the maximum element index plus one.
-</p>
-
-<pre>
-buffer := [10]string{} // len(buffer) == 10
-intSet := [6]int{1, 2, 3, 5} // len(intSet) == 6
-days := [...]string{"Sat", "Sun"} // len(days) == 2
-</pre>
-
-<p>
-A slice literal describes the entire underlying array literal.
-Thus the length and capacity of a slice literal are the maximum
-element index plus one. A slice literal has the form
-</p>
-
-<pre>
-[]T{x1, x2, … xn}
-</pre>
-
-<p>
-and is shorthand for a slice operation applied to an array:
-</p>
-
-<pre>
-tmp := [n]T{x1, x2, … xn}
-tmp[0 : n]
-</pre>
-
-<p>
-Within a composite literal of array, slice, or map type <code>T</code>,
-elements or map keys that are themselves composite literals may elide the respective
-literal type if it is identical to the element or key type of <code>T</code>.
-Similarly, elements or keys that are addresses of composite literals may elide
-the <code>&T</code> when the element or key type is <code>*T</code>.
-</p>
-
-<pre>
-[...]Point{{1.5, -3.5}, {0, 0}} // same as [...]Point{Point{1.5, -3.5}, Point{0, 0}}
-[][]int{{1, 2, 3}, {4, 5}} // same as [][]int{[]int{1, 2, 3}, []int{4, 5}}
-[][]Point{{{0, 1}, {1, 2}}} // same as [][]Point{[]Point{Point{0, 1}, Point{1, 2}}}
-map[string]Point{"orig": {0, 0}} // same as map[string]Point{"orig": Point{0, 0}}
-map[Point]string{{0, 0}: "orig"} // same as map[Point]string{Point{0, 0}: "orig"}
-
-type PPoint *Point
-[2]*Point{{1.5, -3.5}, {}} // same as [2]*Point{&Point{1.5, -3.5}, &Point{}}
-[2]PPoint{{1.5, -3.5}, {}} // same as [2]PPoint{PPoint(&Point{1.5, -3.5}), PPoint(&Point{})}
-</pre>
-
-<p>
-A parsing ambiguity arises when a composite literal using the
-TypeName form of the LiteralType appears as an operand between the
-<a href="#Keywords">keyword</a> and the opening brace of the block
-of an "if", "for", or "switch" statement, and the composite literal
-is not enclosed in parentheses, square brackets, or curly braces.
-In this rare case, the opening brace of the literal is erroneously parsed
-as the one introducing the block of statements. To resolve the ambiguity,
-the composite literal must appear within parentheses.
-</p>
-
-<pre>
-if x == (T{a,b,c}[i]) { … }
-if (x == T{a,b,c}[i]) { … }
-</pre>
-
-<p>
-Examples of valid array, slice, and map literals:
-</p>
-
-<pre>
-// list of prime numbers
-primes := []int{2, 3, 5, 7, 9, 2147483647}
-
-// vowels[ch] is true if ch is a vowel
-vowels := [128]bool{'a': true, 'e': true, 'i': true, 'o': true, 'u': true, 'y': true}
-
-// the array [10]float32{-1, 0, 0, 0, -0.1, -0.1, 0, 0, 0, -1}
-filter := [10]float32{-1, 4: -0.1, -0.1, 9: -1}
-
-// frequencies in Hz for equal-tempered scale (A4 = 440Hz)
-noteFrequency := map[string]float32{
- "C0": 16.35, "D0": 18.35, "E0": 20.60, "F0": 21.83,
- "G0": 24.50, "A0": 27.50, "B0": 30.87,
-}
-</pre>
-
-
-<h3 id="Function_literals">Function literals</h3>
-
-<p>
-A function literal represents an anonymous <a href="#Function_declarations">function</a>.
-</p>
-
-<pre class="ebnf">
-FunctionLit = "func" Signature FunctionBody .
-</pre>
-
-<pre>
-func(a, b int, z float64) bool { return a*b < int(z) }
-</pre>
-
-<p>
-A function literal can be assigned to a variable or invoked directly.
-</p>
-
-<pre>
-f := func(x, y int) int { return x + y }
-func(ch chan int) { ch <- ACK }(replyChan)
-</pre>
-
-<p>
-Function literals are <i>closures</i>: they may refer to variables
-defined in a surrounding function. Those variables are then shared between
-the surrounding function and the function literal, and they survive as long
-as they are accessible.
-</p>
-
-
-<h3 id="Primary_expressions">Primary expressions</h3>
-
-<p>
-Primary expressions are the operands for unary and binary expressions.
-</p>
-
-<pre class="ebnf">
-PrimaryExpr =
- Operand |
- Conversion |
- MethodExpr |
- PrimaryExpr Selector |
- PrimaryExpr Index |
- PrimaryExpr Slice |
- PrimaryExpr TypeAssertion |
- PrimaryExpr Arguments .
-
-Selector = "." identifier .
-Index = "[" Expression "]" .
-Slice = "[" [ Expression ] ":" [ Expression ] "]" |
- "[" [ Expression ] ":" Expression ":" Expression "]" .
-TypeAssertion = "." "(" Type ")" .
-Arguments = "(" [ ( ExpressionList | Type [ "," ExpressionList ] ) [ "..." ] [ "," ] ] ")" .
-</pre>
-
-
-<pre>
-x
-2
-(s + ".txt")
-f(3.1415, true)
-Point{1, 2}
-m["foo"]
-s[i : j + 1]
-obj.color
-f.p[i].x()
-</pre>
-
-
-<h3 id="Selectors">Selectors</h3>
-
-<p>
-For a <a href="#Primary_expressions">primary expression</a> <code>x</code>
-that is not a <a href="#Package_clause">package name</a>, the
-<i>selector expression</i>
-</p>
-
-<pre>
-x.f
-</pre>
-
-<p>
-denotes the field or method <code>f</code> of the value <code>x</code>
-(or sometimes <code>*x</code>; see below).
-The identifier <code>f</code> is called the (field or method) <i>selector</i>;
-it must not be the <a href="#Blank_identifier">blank identifier</a>.
-The type of the selector expression is the type of <code>f</code>.
-If <code>x</code> is a package name, see the section on
-<a href="#Qualified_identifiers">qualified identifiers</a>.
-</p>
-
-<p>
-A selector <code>f</code> may denote a field or method <code>f</code> of
-a type <code>T</code>, or it may refer
-to a field or method <code>f</code> of a nested
-<a href="#Struct_types">embedded field</a> of <code>T</code>.
-The number of embedded fields traversed
-to reach <code>f</code> is called its <i>depth</i> in <code>T</code>.
-The depth of a field or method <code>f</code>
-declared in <code>T</code> is zero.
-The depth of a field or method <code>f</code> declared in
-an embedded field <code>A</code> in <code>T</code> is the
-depth of <code>f</code> in <code>A</code> plus one.
-</p>
-
-<p>
-The following rules apply to selectors:
-</p>
-
-<ol>
-<li>
-For a value <code>x</code> of type <code>T</code> or <code>*T</code>
-where <code>T</code> is not a pointer or interface type,
-<code>x.f</code> denotes the field or method at the shallowest depth
-in <code>T</code> where there
-is such an <code>f</code>.
-If there is not exactly <a href="#Uniqueness_of_identifiers">one <code>f</code></a>
-with shallowest depth, the selector expression is illegal.
-</li>
-
-<li>
-For a value <code>x</code> of type <code>I</code> where <code>I</code>
-is an interface type, <code>x.f</code> denotes the actual method with name
-<code>f</code> of the dynamic value of <code>x</code>.
-If there is no method with name <code>f</code> in the
-<a href="#Method_sets">method set</a> of <code>I</code>, the selector
-expression is illegal.
-</li>
-
-<li>
-As an exception, if the type of <code>x</code> is a <a href="#Type_definitions">defined</a>
-pointer type and <code>(*x).f</code> is a valid selector expression denoting a field
-(but not a method), <code>x.f</code> is shorthand for <code>(*x).f</code>.
-</li>
-
-<li>
-In all other cases, <code>x.f</code> is illegal.
-</li>
-
-<li>
-If <code>x</code> is of pointer type and has the value
-<code>nil</code> and <code>x.f</code> denotes a struct field,
-assigning to or evaluating <code>x.f</code>
-causes a <a href="#Run_time_panics">run-time panic</a>.
-</li>
-
-<li>
-If <code>x</code> is of interface type and has the value
-<code>nil</code>, <a href="#Calls">calling</a> or
-<a href="#Method_values">evaluating</a> the method <code>x.f</code>
-causes a <a href="#Run_time_panics">run-time panic</a>.
-</li>
-</ol>
-
-<p>
-For example, given the declarations:
-</p>
-
-<pre>
-type T0 struct {
- x int
-}
-
-func (*T0) M0()
-
-type T1 struct {
- y int
-}
-
-func (T1) M1()
-
-type T2 struct {
- z int
- T1
- *T0
-}
-
-func (*T2) M2()
-
-type Q *T2
-
-var t T2 // with t.T0 != nil
-var p *T2 // with p != nil and (*p).T0 != nil
-var q Q = p
-</pre>
-
-<p>
-one may write:
-</p>
-
-<pre>
-t.z // t.z
-t.y // t.T1.y
-t.x // (*t.T0).x
-
-p.z // (*p).z
-p.y // (*p).T1.y
-p.x // (*(*p).T0).x
-
-q.x // (*(*q).T0).x (*q).x is a valid field selector
-
-p.M0() // ((*p).T0).M0() M0 expects *T0 receiver
-p.M1() // ((*p).T1).M1() M1 expects T1 receiver
-p.M2() // p.M2() M2 expects *T2 receiver
-t.M2() // (&t).M2() M2 expects *T2 receiver, see section on Calls
-</pre>
-
-<p>
-but the following is invalid:
-</p>
-
-<pre>
-q.M0() // (*q).M0 is valid but not a field selector
-</pre>
-
-
-<h3 id="Method_expressions">Method expressions</h3>
-
-<p>
-If <code>M</code> is in the <a href="#Method_sets">method set</a> of type <code>T</code>,
-<code>T.M</code> is a function that is callable as a regular function
-with the same arguments as <code>M</code> prefixed by an additional
-argument that is the receiver of the method.
-</p>
-
-<pre class="ebnf">
-MethodExpr = ReceiverType "." MethodName .
-ReceiverType = Type .
-</pre>
-
-<p>
-Consider a struct type <code>T</code> with two methods,
-<code>Mv</code>, whose receiver is of type <code>T</code>, and
-<code>Mp</code>, whose receiver is of type <code>*T</code>.
-</p>
-
-<pre>
-type T struct {
- a int
-}
-func (tv T) Mv(a int) int { return 0 } // value receiver
-func (tp *T) Mp(f float32) float32 { return 1 } // pointer receiver
-
-var t T
-</pre>
-
-<p>
-The expression
-</p>
-
-<pre>
-T.Mv
-</pre>
-
-<p>
-yields a function equivalent to <code>Mv</code> but
-with an explicit receiver as its first argument; it has signature
-</p>
-
-<pre>
-func(tv T, a int) int
-</pre>
-
-<p>
-That function may be called normally with an explicit receiver, so
-these five invocations are equivalent:
-</p>
-
-<pre>
-t.Mv(7)
-T.Mv(t, 7)
-(T).Mv(t, 7)
-f1 := T.Mv; f1(t, 7)
-f2 := (T).Mv; f2(t, 7)
-</pre>
-
-<p>
-Similarly, the expression
-</p>
-
-<pre>
-(*T).Mp
-</pre>
-
-<p>
-yields a function value representing <code>Mp</code> with signature
-</p>
-
-<pre>
-func(tp *T, f float32) float32
-</pre>
-
-<p>
-For a method with a value receiver, one can derive a function
-with an explicit pointer receiver, so
-</p>
-
-<pre>
-(*T).Mv
-</pre>
-
-<p>
-yields a function value representing <code>Mv</code> with signature
-</p>
-
-<pre>
-func(tv *T, a int) int
-</pre>
-
-<p>
-Such a function indirects through the receiver to create a value
-to pass as the receiver to the underlying method;
-the method does not overwrite the value whose address is passed in
-the function call.
-</p>
-
-<p>
-The final case, a value-receiver function for a pointer-receiver method,
-is illegal because pointer-receiver methods are not in the method set
-of the value type.
-</p>
-
-<p>
-Function values derived from methods are called with function call syntax;
-the receiver is provided as the first argument to the call.
-That is, given <code>f := T.Mv</code>, <code>f</code> is invoked
-as <code>f(t, 7)</code> not <code>t.f(7)</code>.
-To construct a function that binds the receiver, use a
-<a href="#Function_literals">function literal</a> or
-<a href="#Method_values">method value</a>.
-</p>
-
-<p>
-It is legal to derive a function value from a method of an interface type.
-The resulting function takes an explicit receiver of that interface type.
-</p>
-
-<h3 id="Method_values">Method values</h3>
-
-<p>
-If the expression <code>x</code> has static type <code>T</code> and
-<code>M</code> is in the <a href="#Method_sets">method set</a> of type <code>T</code>,
-<code>x.M</code> is called a <i>method value</i>.
-The method value <code>x.M</code> is a function value that is callable
-with the same arguments as a method call of <code>x.M</code>.
-The expression <code>x</code> is evaluated and saved during the evaluation of the
-method value; the saved copy is then used as the receiver in any calls,
-which may be executed later.
-</p>
-
-<pre>
-type S struct { *T }
-type T int
-func (t T) M() { print(t) }
-
-t := new(T)
-s := S{T: t}
-f := t.M // receiver *t is evaluated and stored in f
-g := s.M // receiver *(s.T) is evaluated and stored in g
-*t = 42 // does not affect stored receivers in f and g
-</pre>
-
-<p>
-The type <code>T</code> may be an interface or non-interface type.
-</p>
-
-<p>
-As in the discussion of <a href="#Method_expressions">method expressions</a> above,
-consider a struct type <code>T</code> with two methods,
-<code>Mv</code>, whose receiver is of type <code>T</code>, and
-<code>Mp</code>, whose receiver is of type <code>*T</code>.
-</p>
-
-<pre>
-type T struct {
- a int
-}
-func (tv T) Mv(a int) int { return 0 } // value receiver
-func (tp *T) Mp(f float32) float32 { return 1 } // pointer receiver
-
-var t T
-var pt *T
-func makeT() T
-</pre>
-
-<p>
-The expression
-</p>
-
-<pre>
-t.Mv
-</pre>
-
-<p>
-yields a function value of type
-</p>
-
-<pre>
-func(int) int
-</pre>
-
-<p>
-These two invocations are equivalent:
-</p>
-
-<pre>
-t.Mv(7)
-f := t.Mv; f(7)
-</pre>
-
-<p>
-Similarly, the expression
-</p>
-
-<pre>
-pt.Mp
-</pre>
-
-<p>
-yields a function value of type
-</p>
-
-<pre>
-func(float32) float32
-</pre>
-
-<p>
-As with <a href="#Selectors">selectors</a>, a reference to a non-interface method with a value receiver
-using a pointer will automatically dereference that pointer: <code>pt.Mv</code> is equivalent to <code>(*pt).Mv</code>.
-</p>
-
-<p>
-As with <a href="#Calls">method calls</a>, a reference to a non-interface method with a pointer receiver
-using an addressable value will automatically take the address of that value: <code>t.Mp</code> is equivalent to <code>(&t).Mp</code>.
-</p>
-
-<pre>
-f := t.Mv; f(7) // like t.Mv(7)
-f := pt.Mp; f(7) // like pt.Mp(7)
-f := pt.Mv; f(7) // like (*pt).Mv(7)
-f := t.Mp; f(7) // like (&t).Mp(7)
-f := makeT().Mp // invalid: result of makeT() is not addressable
-</pre>
-
-<p>
-Although the examples above use non-interface types, it is also legal to create a method value
-from a value of interface type.
-</p>
-
-<pre>
-var i interface { M(int) } = myVal
-f := i.M; f(7) // like i.M(7)
-</pre>
-
-
-<h3 id="Index_expressions">Index expressions</h3>
-
-<p>
-A primary expression of the form
-</p>
-
-<pre>
-a[x]
-</pre>
-
-<p>
-denotes the element of the array, pointer to array, slice, string or map <code>a</code> indexed by <code>x</code>.
-The value <code>x</code> is called the <i>index</i> or <i>map key</i>, respectively.
-The following rules apply:
-</p>
-
-<p>
-If <code>a</code> is not a map:
-</p>
-<ul>
- <li>the index <code>x</code> must be of integer type or an untyped constant</li>
- <li>a constant index must be non-negative and
- <a href="#Representability">representable</a> by a value of type <code>int</code></li>
- <li>a constant index that is untyped is given type <code>int</code></li>
- <li>the index <code>x</code> is <i>in range</i> if <code>0 <= x < len(a)</code>,
- otherwise it is <i>out of range</i></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Array_types">array type</a> <code>A</code>:
-</p>
-<ul>
- <li>a <a href="#Constants">constant</a> index must be in range</li>
- <li>if <code>x</code> is out of range at run time,
- a <a href="#Run_time_panics">run-time panic</a> occurs</li>
- <li><code>a[x]</code> is the array element at index <code>x</code> and the type of
- <code>a[x]</code> is the element type of <code>A</code></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Pointer_types">pointer</a> to array type:
-</p>
-<ul>
- <li><code>a[x]</code> is shorthand for <code>(*a)[x]</code></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Slice_types">slice type</a> <code>S</code>:
-</p>
-<ul>
- <li>if <code>x</code> is out of range at run time,
- a <a href="#Run_time_panics">run-time panic</a> occurs</li>
- <li><code>a[x]</code> is the slice element at index <code>x</code> and the type of
- <code>a[x]</code> is the element type of <code>S</code></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#String_types">string type</a>:
-</p>
-<ul>
- <li>a <a href="#Constants">constant</a> index must be in range
- if the string <code>a</code> is also constant</li>
- <li>if <code>x</code> is out of range at run time,
- a <a href="#Run_time_panics">run-time panic</a> occurs</li>
- <li><code>a[x]</code> is the non-constant byte value at index <code>x</code> and the type of
- <code>a[x]</code> is <code>byte</code></li>
- <li><code>a[x]</code> may not be assigned to</li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Map_types">map type</a> <code>M</code>:
-</p>
-<ul>
- <li><code>x</code>'s type must be
- <a href="#Assignability">assignable</a>
- to the key type of <code>M</code></li>
- <li>if the map contains an entry with key <code>x</code>,
- <code>a[x]</code> is the map element with key <code>x</code>
- and the type of <code>a[x]</code> is the element type of <code>M</code></li>
- <li>if the map is <code>nil</code> or does not contain such an entry,
- <code>a[x]</code> is the <a href="#The_zero_value">zero value</a>
- for the element type of <code>M</code></li>
-</ul>
-
-<p>
-Otherwise <code>a[x]</code> is illegal.
-</p>
-
-<p>
-An index expression on a map <code>a</code> of type <code>map[K]V</code>
-used in an <a href="#Assignments">assignment</a> or initialization of the special form
-</p>
-
-<pre>
-v, ok = a[x]
-v, ok := a[x]
-var v, ok = a[x]
-</pre>
-
-<p>
-yields an additional untyped boolean value. The value of <code>ok</code> is
-<code>true</code> if the key <code>x</code> is present in the map, and
-<code>false</code> otherwise.
-</p>
-
-<p>
-Assigning to an element of a <code>nil</code> map causes a
-<a href="#Run_time_panics">run-time panic</a>.
-</p>
-
-
-<h3 id="Slice_expressions">Slice expressions</h3>
-
-<p>
-Slice expressions construct a substring or slice from a string, array, pointer
-to array, or slice. There are two variants: a simple form that specifies a low
-and high bound, and a full form that also specifies a bound on the capacity.
-</p>
-
-<h4>Simple slice expressions</h4>
-
-<p>
-For a string, array, pointer to array, or slice <code>a</code>, the primary expression
-</p>
-
-<pre>
-a[low : high]
-</pre>
-
-<p>
-constructs a substring or slice. The <i>indices</i> <code>low</code> and
-<code>high</code> select which elements of operand <code>a</code> appear
-in the result. The result has indices starting at 0 and length equal to
-<code>high</code> - <code>low</code>.
-After slicing the array <code>a</code>
-</p>
-
-<pre>
-a := [5]int{1, 2, 3, 4, 5}
-s := a[1:4]
-</pre>
-
-<p>
-the slice <code>s</code> has type <code>[]int</code>, length 3, capacity 4, and elements
-</p>
-
-<pre>
-s[0] == 2
-s[1] == 3
-s[2] == 4
-</pre>
-
-<p>
-For convenience, any of the indices may be omitted. A missing <code>low</code>
-index defaults to zero; a missing <code>high</code> index defaults to the length of the
-sliced operand:
-</p>
-
-<pre>
-a[2:] // same as a[2 : len(a)]
-a[:3] // same as a[0 : 3]
-a[:] // same as a[0 : len(a)]
-</pre>
-
-<p>
-If <code>a</code> is a pointer to an array, <code>a[low : high]</code> is shorthand for
-<code>(*a)[low : high]</code>.
-</p>
-
-<p>
-For arrays or strings, the indices are <i>in range</i> if
-<code>0</code> <= <code>low</code> <= <code>high</code> <= <code>len(a)</code>,
-otherwise they are <i>out of range</i>.
-For slices, the upper index bound is the slice capacity <code>cap(a)</code> rather than the length.
-A <a href="#Constants">constant</a> index must be non-negative and
-<a href="#Representability">representable</a> by a value of type
-<code>int</code>; for arrays or constant strings, constant indices must also be in range.
-If both indices are constant, they must satisfy <code>low <= high</code>.
-If the indices are out of range at run time, a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<p>
-Except for <a href="#Constants">untyped strings</a>, if the sliced operand is a string or slice,
-the result of the slice operation is a non-constant value of the same type as the operand.
-For untyped string operands the result is a non-constant value of type <code>string</code>.
-If the sliced operand is an array, it must be <a href="#Address_operators">addressable</a>
-and the result of the slice operation is a slice with the same element type as the array.
-</p>
-
-<p>
-If the sliced operand of a valid slice expression is a <code>nil</code> slice, the result
-is a <code>nil</code> slice. Otherwise, if the result is a slice, it shares its underlying
-array with the operand.
-</p>
-
-<pre>
-var a [10]int
-s1 := a[3:7] // underlying array of s1 is array a; &s1[2] == &a[5]
-s2 := s1[1:4] // underlying array of s2 is underlying array of s1 which is array a; &s2[1] == &a[5]
-s2[1] = 42 // s2[1] == s1[2] == a[5] == 42; they all refer to the same underlying array element
-</pre>
-
-
-<h4>Full slice expressions</h4>
-
-<p>
-For an array, pointer to array, or slice <code>a</code> (but not a string), the primary expression
-</p>
-
-<pre>
-a[low : high : max]
-</pre>
-
-<p>
-constructs a slice of the same type, and with the same length and elements as the simple slice
-expression <code>a[low : high]</code>. Additionally, it controls the resulting slice's capacity
-by setting it to <code>max - low</code>. Only the first index may be omitted; it defaults to 0.
-After slicing the array <code>a</code>
-</p>
-
-<pre>
-a := [5]int{1, 2, 3, 4, 5}
-t := a[1:3:5]
-</pre>
-
-<p>
-the slice <code>t</code> has type <code>[]int</code>, length 2, capacity 4, and elements
-</p>
-
-<pre>
-t[0] == 2
-t[1] == 3
-</pre>
-
-<p>
-As for simple slice expressions, if <code>a</code> is a pointer to an array,
-<code>a[low : high : max]</code> is shorthand for <code>(*a)[low : high : max]</code>.
-If the sliced operand is an array, it must be <a href="#Address_operators">addressable</a>.
-</p>
-
-<p>
-The indices are <i>in range</i> if <code>0 <= low <= high <= max <= cap(a)</code>,
-otherwise they are <i>out of range</i>.
-A <a href="#Constants">constant</a> index must be non-negative and
-<a href="#Representability">representable</a> by a value of type
-<code>int</code>; for arrays, constant indices must also be in range.
-If multiple indices are constant, the constants that are present must be in range relative to each
-other.
-If the indices are out of range at run time, a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<h3 id="Type_assertions">Type assertions</h3>
-
-<p>
-For an expression <code>x</code> of <a href="#Interface_types">interface type</a>
-and a type <code>T</code>, the primary expression
-</p>
-
-<pre>
-x.(T)
-</pre>
-
-<p>
-asserts that <code>x</code> is not <code>nil</code>
-and that the value stored in <code>x</code> is of type <code>T</code>.
-The notation <code>x.(T)</code> is called a <i>type assertion</i>.
-</p>
-<p>
-More precisely, if <code>T</code> is not an interface type, <code>x.(T)</code> asserts
-that the dynamic type of <code>x</code> is <a href="#Type_identity">identical</a>
-to the type <code>T</code>.
-In this case, <code>T</code> must <a href="#Method_sets">implement</a> the (interface) type of <code>x</code>;
-otherwise the type assertion is invalid since it is not possible for <code>x</code>
-to store a value of type <code>T</code>.
-If <code>T</code> is an interface type, <code>x.(T)</code> asserts that the dynamic type
-of <code>x</code> implements the interface <code>T</code>.
-</p>
-<p>
-If the type assertion holds, the value of the expression is the value
-stored in <code>x</code> and its type is <code>T</code>. If the type assertion is false,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-In other words, even though the dynamic type of <code>x</code>
-is known only at run time, the type of <code>x.(T)</code> is
-known to be <code>T</code> in a correct program.
-</p>
-
-<pre>
-var x interface{} = 7 // x has dynamic type int and value 7
-i := x.(int) // i has type int and value 7
-
-type I interface { m() }
-
-func f(y I) {
- s := y.(string) // illegal: string does not implement I (missing method m)
- r := y.(io.Reader) // r has type io.Reader and the dynamic type of y must implement both I and io.Reader
- …
-}
-</pre>
-
-<p>
-A type assertion used in an <a href="#Assignments">assignment</a> or initialization of the special form
-</p>
-
-<pre>
-v, ok = x.(T)
-v, ok := x.(T)
-var v, ok = x.(T)
-var v, ok interface{} = x.(T) // dynamic types of v and ok are T and bool
-</pre>
-
-<p>
-yields an additional untyped boolean value. The value of <code>ok</code> is <code>true</code>
-if the assertion holds. Otherwise it is <code>false</code> and the value of <code>v</code> is
-the <a href="#The_zero_value">zero value</a> for type <code>T</code>.
-No <a href="#Run_time_panics">run-time panic</a> occurs in this case.
-</p>
-
-
-<h3 id="Calls">Calls</h3>
-
-<p>
-Given an expression <code>f</code> of function type
-<code>F</code>,
-</p>
-
-<pre>
-f(a1, a2, … an)
-</pre>
-
-<p>
-calls <code>f</code> with arguments <code>a1, a2, … an</code>.
-Except for one special case, arguments must be single-valued expressions
-<a href="#Assignability">assignable</a> to the parameter types of
-<code>F</code> and are evaluated before the function is called.
-The type of the expression is the result type
-of <code>F</code>.
-A method invocation is similar but the method itself
-is specified as a selector upon a value of the receiver type for
-the method.
-</p>
-
-<pre>
-math.Atan2(x, y) // function call
-var pt *Point
-pt.Scale(3.5) // method call with receiver pt
-</pre>
-
-<p>
-In a function call, the function value and arguments are evaluated in
-<a href="#Order_of_evaluation">the usual order</a>.
-After they are evaluated, the parameters of the call are passed by value to the function
-and the called function begins execution.
-The return parameters of the function are passed by value
-back to the caller when the function returns.
-</p>
-
-<p>
-Calling a <code>nil</code> function value
-causes a <a href="#Run_time_panics">run-time panic</a>.
-</p>
-
-<p>
-As a special case, if the return values of a function or method
-<code>g</code> are equal in number and individually
-assignable to the parameters of another function or method
-<code>f</code>, then the call <code>f(g(<i>parameters_of_g</i>))</code>
-will invoke <code>f</code> after binding the return values of
-<code>g</code> to the parameters of <code>f</code> in order. The call
-of <code>f</code> must contain no parameters other than the call of <code>g</code>,
-and <code>g</code> must have at least one return value.
-If <code>f</code> has a final <code>...</code> parameter, it is
-assigned the return values of <code>g</code> that remain after
-assignment of regular parameters.
-</p>
-
-<pre>
-func Split(s string, pos int) (string, string) {
- return s[0:pos], s[pos:]
-}
-
-func Join(s, t string) string {
- return s + t
-}
-
-if Join(Split(value, len(value)/2)) != value {
- log.Panic("test fails")
-}
-</pre>
-
-<p>
-A method call <code>x.m()</code> is valid if the <a href="#Method_sets">method set</a>
-of (the type of) <code>x</code> contains <code>m</code> and the
-argument list can be assigned to the parameter list of <code>m</code>.
-If <code>x</code> is <a href="#Address_operators">addressable</a> and <code>&x</code>'s method
-set contains <code>m</code>, <code>x.m()</code> is shorthand
-for <code>(&x).m()</code>:
-</p>
-
-<pre>
-var p Point
-p.Scale(3.5)
-</pre>
-
-<p>
-There is no distinct method type and there are no method literals.
-</p>
-
-<h3 id="Passing_arguments_to_..._parameters">Passing arguments to <code>...</code> parameters</h3>
-
-<p>
-If <code>f</code> is <a href="#Function_types">variadic</a> with a final
-parameter <code>p</code> of type <code>...T</code>, then within <code>f</code>
-the type of <code>p</code> is equivalent to type <code>[]T</code>.
-If <code>f</code> is invoked with no actual arguments for <code>p</code>,
-the value passed to <code>p</code> is <code>nil</code>.
-Otherwise, the value passed is a new slice
-of type <code>[]T</code> with a new underlying array whose successive elements
-are the actual arguments, which all must be <a href="#Assignability">assignable</a>
-to <code>T</code>. The length and capacity of the slice is therefore
-the number of arguments bound to <code>p</code> and may differ for each
-call site.
-</p>
-
-<p>
-Given the function and calls
-</p>
-<pre>
-func Greeting(prefix string, who ...string)
-Greeting("nobody")
-Greeting("hello:", "Joe", "Anna", "Eileen")
-</pre>
-
-<p>
-within <code>Greeting</code>, <code>who</code> will have the value
-<code>nil</code> in the first call, and
-<code>[]string{"Joe", "Anna", "Eileen"}</code> in the second.
-</p>
-
-<p>
-If the final argument is assignable to a slice type <code>[]T</code> and
-is followed by <code>...</code>, it is passed unchanged as the value
-for a <code>...T</code> parameter. In this case no new slice is created.
-</p>
-
-<p>
-Given the slice <code>s</code> and call
-</p>
-
-<pre>
-s := []string{"James", "Jasmine"}
-Greeting("goodbye:", s...)
-</pre>
-
-<p>
-within <code>Greeting</code>, <code>who</code> will have the same value as <code>s</code>
-with the same underlying array.
-</p>
-
-
-<h3 id="Operators">Operators</h3>
-
-<p>
-Operators combine operands into expressions.
-</p>
-
-<pre class="ebnf">
-Expression = UnaryExpr | Expression binary_op Expression .
-UnaryExpr = PrimaryExpr | unary_op UnaryExpr .
-
-binary_op = "||" | "&&" | rel_op | add_op | mul_op .
-rel_op = "==" | "!=" | "<" | "<=" | ">" | ">=" .
-add_op = "+" | "-" | "|" | "^" .
-mul_op = "*" | "/" | "%" | "<<" | ">>" | "&" | "&^" .
-
-unary_op = "+" | "-" | "!" | "^" | "*" | "&" | "<-" .
-</pre>
-
-<p>
-Comparisons are discussed <a href="#Comparison_operators">elsewhere</a>.
-For other binary operators, the operand types must be <a href="#Type_identity">identical</a>
-unless the operation involves shifts or untyped <a href="#Constants">constants</a>.
-For operations involving constants only, see the section on
-<a href="#Constant_expressions">constant expressions</a>.
-</p>
-
-<p>
-Except for shift operations, if one operand is an untyped <a href="#Constants">constant</a>
-and the other operand is not, the constant is implicitly <a href="#Conversions">converted</a>
-to the type of the other operand.
-</p>
-
-<p>
-The right operand in a shift expression must have integer type
-or be an untyped constant <a href="#Representability">representable</a> by a
-value of type <code>uint</code>.
-If the left operand of a non-constant shift expression is an untyped constant,
-it is first implicitly converted to the type it would assume if the shift expression were
-replaced by its left operand alone.
-</p>
-
-<pre>
-var a [1024]byte
-var s uint = 33
-
-// The results of the following examples are given for 64-bit ints.
-var i = 1<<s // 1 has type int
-var j int32 = 1<<s // 1 has type int32; j == 0
-var k = uint64(1<<s) // 1 has type uint64; k == 1<<33
-var m int = 1.0<<s // 1.0 has type int; m == 1<<33
-var n = 1.0<<s == j // 1.0 has type int32; n == true
-var o = 1<<s == 2<<s // 1 and 2 have type int; o == false
-var p = 1<<s == 1<<33 // 1 has type int; p == true
-var u = 1.0<<s // illegal: 1.0 has type float64, cannot shift
-var u1 = 1.0<<s != 0 // illegal: 1.0 has type float64, cannot shift
-var u2 = 1<<s != 1.0 // illegal: 1 has type float64, cannot shift
-var v float32 = 1<<s // illegal: 1 has type float32, cannot shift
-var w int64 = 1.0<<33 // 1.0<<33 is a constant shift expression; w == 1<<33
-var x = a[1.0<<s] // panics: 1.0 has type int, but 1<<33 overflows array bounds
-var b = make([]byte, 1.0<<s) // 1.0 has type int; len(b) == 1<<33
-
-// The results of the following examples are given for 32-bit ints,
-// which means the shifts will overflow.
-var mm int = 1.0<<s // 1.0 has type int; mm == 0
-var oo = 1<<s == 2<<s // 1 and 2 have type int; oo == true
-var pp = 1<<s == 1<<33 // illegal: 1 has type int, but 1<<33 overflows int
-var xx = a[1.0<<s] // 1.0 has type int; xx == a[0]
-var bb = make([]byte, 1.0<<s) // 1.0 has type int; len(bb) == 0
-</pre>
-
-<h4 id="Operator_precedence">Operator precedence</h4>
-<p>
-Unary operators have the highest precedence.
-As the <code>++</code> and <code>--</code> operators form
-statements, not expressions, they fall
-outside the operator hierarchy.
-As a consequence, statement <code>*p++</code> is the same as <code>(*p)++</code>.
-<p>
-There are five precedence levels for binary operators.
-Multiplication operators bind strongest, followed by addition
-operators, comparison operators, <code>&&</code> (logical AND),
-and finally <code>||</code> (logical OR):
-</p>
-
-<pre class="grammar">
-Precedence Operator
- 5 * / % << >> & &^
- 4 + - | ^
- 3 == != < <= > >=
- 2 &&
- 1 ||
-</pre>
-
-<p>
-Binary operators of the same precedence associate from left to right.
-For instance, <code>x / y * z</code> is the same as <code>(x / y) * z</code>.
-</p>
-
-<pre>
-+x
-23 + 3*x[i]
-x <= f()
-^a >> b
-f() || g()
-x == y+1 && <-chanInt > 0
-</pre>
-
-
-<h3 id="Arithmetic_operators">Arithmetic operators</h3>
-<p>
-Arithmetic operators apply to numeric values and yield a result of the same
-type as the first operand. The four standard arithmetic operators (<code>+</code>,
-<code>-</code>, <code>*</code>, <code>/</code>) apply to integer,
-floating-point, and complex types; <code>+</code> also applies to strings.
-The bitwise logical and shift operators apply to integers only.
-</p>
-
-<pre class="grammar">
-+ sum integers, floats, complex values, strings
-- difference integers, floats, complex values
-* product integers, floats, complex values
-/ quotient integers, floats, complex values
-% remainder integers
-
-& bitwise AND integers
-| bitwise OR integers
-^ bitwise XOR integers
-&^ bit clear (AND NOT) integers
-
-<< left shift integer << integer >= 0
->> right shift integer >> integer >= 0
-</pre>
-
-
-<h4 id="Integer_operators">Integer operators</h4>
-
-<p>
-For two integer values <code>x</code> and <code>y</code>, the integer quotient
-<code>q = x / y</code> and remainder <code>r = x % y</code> satisfy the following
-relationships:
-</p>
-
-<pre>
-x = q*y + r and |r| < |y|
-</pre>
-
-<p>
-with <code>x / y</code> truncated towards zero
-(<a href="https://en.wikipedia.org/wiki/Modulo_operation">"truncated division"</a>).
-</p>
-
-<pre>
- x y x / y x % y
- 5 3 1 2
--5 3 -1 -2
- 5 -3 -1 2
--5 -3 1 -2
-</pre>
-
-<p>
-The one exception to this rule is that if the dividend <code>x</code> is
-the most negative value for the int type of <code>x</code>, the quotient
-<code>q = x / -1</code> is equal to <code>x</code> (and <code>r = 0</code>)
-due to two's-complement <a href="#Integer_overflow">integer overflow</a>:
-</p>
-
-<pre>
- x, q
-int8 -128
-int16 -32768
-int32 -2147483648
-int64 -9223372036854775808
-</pre>
-
-<p>
-If the divisor is a <a href="#Constants">constant</a>, it must not be zero.
-If the divisor is zero at run time, a <a href="#Run_time_panics">run-time panic</a> occurs.
-If the dividend is non-negative and the divisor is a constant power of 2,
-the division may be replaced by a right shift, and computing the remainder may
-be replaced by a bitwise AND operation:
-</p>
-
-<pre>
- x x / 4 x % 4 x >> 2 x & 3
- 11 2 3 2 3
--11 -2 -3 -3 1
-</pre>
-
-<p>
-The shift operators shift the left operand by the shift count specified by the
-right operand, which must be non-negative. If the shift count is negative at run time,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-The shift operators implement arithmetic shifts if the left operand is a signed
-integer and logical shifts if it is an unsigned integer.
-There is no upper limit on the shift count. Shifts behave
-as if the left operand is shifted <code>n</code> times by 1 for a shift
-count of <code>n</code>.
-As a result, <code>x << 1</code> is the same as <code>x*2</code>
-and <code>x >> 1</code> is the same as
-<code>x/2</code> but truncated towards negative infinity.
-</p>
-
-<p>
-For integer operands, the unary operators
-<code>+</code>, <code>-</code>, and <code>^</code> are defined as
-follows:
-</p>
-
-<pre class="grammar">
-+x is 0 + x
--x negation is 0 - x
-^x bitwise complement is m ^ x with m = "all bits set to 1" for unsigned x
- and m = -1 for signed x
-</pre>
-
-
-<h4 id="Integer_overflow">Integer overflow</h4>
-
-<p>
-For unsigned integer values, the operations <code>+</code>,
-<code>-</code>, <code>*</code>, and <code><<</code> are
-computed modulo 2<sup><i>n</i></sup>, where <i>n</i> is the bit width of
-the <a href="#Numeric_types">unsigned integer</a>'s type.
-Loosely speaking, these unsigned integer operations
-discard high bits upon overflow, and programs may rely on "wrap around".
-</p>
-<p>
-For signed integers, the operations <code>+</code>,
-<code>-</code>, <code>*</code>, <code>/</code>, and <code><<</code> may legally
-overflow and the resulting value exists and is deterministically defined
-by the signed integer representation, the operation, and its operands.
-Overflow does not cause a <a href="#Run_time_panics">run-time panic</a>.
-A compiler may not optimize code under the assumption that overflow does
-not occur. For instance, it may not assume that <code>x < x + 1</code> is always true.
-</p>
-
-
-<h4 id="Floating_point_operators">Floating-point operators</h4>
-
-<p>
-For floating-point and complex numbers,
-<code>+x</code> is the same as <code>x</code>,
-while <code>-x</code> is the negation of <code>x</code>.
-The result of a floating-point or complex division by zero is not specified beyond the
-IEEE-754 standard; whether a <a href="#Run_time_panics">run-time panic</a>
-occurs is implementation-specific.
-</p>
-
-<p>
-An implementation may combine multiple floating-point operations into a single
-fused operation, possibly across statements, and produce a result that differs
-from the value obtained by executing and rounding the instructions individually.
-An explicit floating-point type <a href="#Conversions">conversion</a> rounds to
-the precision of the target type, preventing fusion that would discard that rounding.
-</p>
-
-<p>
-For instance, some architectures provide a "fused multiply and add" (FMA) instruction
-that computes <code>x*y + z</code> without rounding the intermediate result <code>x*y</code>.
-These examples show when a Go implementation can use that instruction:
-</p>
-
-<pre>
-// FMA allowed for computing r, because x*y is not explicitly rounded:
-r = x*y + z
-r = z; r += x*y
-t = x*y; r = t + z
-*p = x*y; r = *p + z
-r = x*y + float64(z)
-
-// FMA disallowed for computing r, because it would omit rounding of x*y:
-r = float64(x*y) + z
-r = z; r += float64(x*y)
-t = float64(x*y); r = t + z
-</pre>
-
-<h4 id="String_concatenation">String concatenation</h4>
-
-<p>
-Strings can be concatenated using the <code>+</code> operator
-or the <code>+=</code> assignment operator:
-</p>
-
-<pre>
-s := "hi" + string(c)
-s += " and good bye"
-</pre>
-
-<p>
-String addition creates a new string by concatenating the operands.
-</p>
-
-
-<h3 id="Comparison_operators">Comparison operators</h3>
-
-<p>
-Comparison operators compare two operands and yield an untyped boolean value.
-</p>
-
-<pre class="grammar">
-== equal
-!= not equal
-< less
-<= less or equal
-> greater
->= greater or equal
-</pre>
-
-<p>
-In any comparison, the first operand
-must be <a href="#Assignability">assignable</a>
-to the type of the second operand, or vice versa.
-</p>
-<p>
-The equality operators <code>==</code> and <code>!=</code> apply
-to operands that are <i>comparable</i>.
-The ordering operators <code><</code>, <code><=</code>, <code>></code>, and <code>>=</code>
-apply to operands that are <i>ordered</i>.
-These terms and the result of the comparisons are defined as follows:
-</p>
-
-<ul>
- <li>
- Boolean values are comparable.
- Two boolean values are equal if they are either both
- <code>true</code> or both <code>false</code>.
- </li>
-
- <li>
- Integer values are comparable and ordered, in the usual way.
- </li>
-
- <li>
- Floating-point values are comparable and ordered,
- as defined by the IEEE-754 standard.
- </li>
-
- <li>
- Complex values are comparable.
- Two complex values <code>u</code> and <code>v</code> are
- equal if both <code>real(u) == real(v)</code> and
- <code>imag(u) == imag(v)</code>.
- </li>
-
- <li>
- String values are comparable and ordered, lexically byte-wise.
- </li>
-
- <li>
- Pointer values are comparable.
- Two pointer values are equal if they point to the same variable or if both have value <code>nil</code>.
- Pointers to distinct <a href="#Size_and_alignment_guarantees">zero-size</a> variables may or may not be equal.
- </li>
-
- <li>
- Channel values are comparable.
- Two channel values are equal if they were created by the same call to
- <a href="#Making_slices_maps_and_channels"><code>make</code></a>
- or if both have value <code>nil</code>.
- </li>
-
- <li>
- Interface values are comparable.
- Two interface values are equal if they have <a href="#Type_identity">identical</a> dynamic types
- and equal dynamic values or if both have value <code>nil</code>.
- </li>
-
- <li>
- A value <code>x</code> of non-interface type <code>X</code> and
- a value <code>t</code> of interface type <code>T</code> are comparable when values
- of type <code>X</code> are comparable and
- <code>X</code> implements <code>T</code>.
- They are equal if <code>t</code>'s dynamic type is identical to <code>X</code>
- and <code>t</code>'s dynamic value is equal to <code>x</code>.
- </li>
-
- <li>
- Struct values are comparable if all their fields are comparable.
- Two struct values are equal if their corresponding
- non-<a href="#Blank_identifier">blank</a> fields are equal.
- </li>
-
- <li>
- Array values are comparable if values of the array element type are comparable.
- Two array values are equal if their corresponding elements are equal.
- </li>
-</ul>
-
-<p>
-A comparison of two interface values with identical dynamic types
-causes a <a href="#Run_time_panics">run-time panic</a> if values
-of that type are not comparable. This behavior applies not only to direct interface
-value comparisons but also when comparing arrays of interface values
-or structs with interface-valued fields.
-</p>
-
-<p>
-Slice, map, and function values are not comparable.
-However, as a special case, a slice, map, or function value may
-be compared to the predeclared identifier <code>nil</code>.
-Comparison of pointer, channel, and interface values to <code>nil</code>
-is also allowed and follows from the general rules above.
-</p>
-
-<pre>
-const c = 3 < 4 // c is the untyped boolean constant true
-
-type MyBool bool
-var x, y int
-var (
- // The result of a comparison is an untyped boolean.
- // The usual assignment rules apply.
- b3 = x == y // b3 has type bool
- b4 bool = x == y // b4 has type bool
- b5 MyBool = x == y // b5 has type MyBool
-)
-</pre>
-
-<h3 id="Logical_operators">Logical operators</h3>
-
-<p>
-Logical operators apply to <a href="#Boolean_types">boolean</a> values
-and yield a result of the same type as the operands.
-The right operand is evaluated conditionally.
-</p>
-
-<pre class="grammar">
-&& conditional AND p && q is "if p then q else false"
-|| conditional OR p || q is "if p then true else q"
-! NOT !p is "not p"
-</pre>
-
-
-<h3 id="Address_operators">Address operators</h3>
-
-<p>
-For an operand <code>x</code> of type <code>T</code>, the address operation
-<code>&x</code> generates a pointer of type <code>*T</code> to <code>x</code>.
-The operand must be <i>addressable</i>,
-that is, either a variable, pointer indirection, or slice indexing
-operation; or a field selector of an addressable struct operand;
-or an array indexing operation of an addressable array.
-As an exception to the addressability requirement, <code>x</code> may also be a
-(possibly parenthesized)
-<a href="#Composite_literals">composite literal</a>.
-If the evaluation of <code>x</code> would cause a <a href="#Run_time_panics">run-time panic</a>,
-then the evaluation of <code>&x</code> does too.
-</p>
-
-<p>
-For an operand <code>x</code> of pointer type <code>*T</code>, the pointer
-indirection <code>*x</code> denotes the <a href="#Variables">variable</a> of type <code>T</code> pointed
-to by <code>x</code>.
-If <code>x</code> is <code>nil</code>, an attempt to evaluate <code>*x</code>
-will cause a <a href="#Run_time_panics">run-time panic</a>.
-</p>
-
-<pre>
-&x
-&a[f(2)]
-&Point{2, 3}
-*p
-*pf(x)
-
-var x *int = nil
-*x // causes a run-time panic
-&*x // causes a run-time panic
-</pre>
-
-
-<h3 id="Receive_operator">Receive operator</h3>
-
-<p>
-For an operand <code>ch</code> of <a href="#Channel_types">channel type</a>,
-the value of the receive operation <code><-ch</code> is the value received
-from the channel <code>ch</code>. The channel direction must permit receive operations,
-and the type of the receive operation is the element type of the channel.
-The expression blocks until a value is available.
-Receiving from a <code>nil</code> channel blocks forever.
-A receive operation on a <a href="#Close">closed</a> channel can always proceed
-immediately, yielding the element type's <a href="#The_zero_value">zero value</a>
-after any previously sent values have been received.
-</p>
-
-<pre>
-v1 := <-ch
-v2 = <-ch
-f(<-ch)
-<-strobe // wait until clock pulse and discard received value
-</pre>
-
-<p>
-A receive expression used in an <a href="#Assignments">assignment</a> or initialization of the special form
-</p>
-
-<pre>
-x, ok = <-ch
-x, ok := <-ch
-var x, ok = <-ch
-var x, ok T = <-ch
-</pre>
-
-<p>
-yields an additional untyped boolean result reporting whether the
-communication succeeded. The value of <code>ok</code> is <code>true</code>
-if the value received was delivered by a successful send operation to the
-channel, or <code>false</code> if it is a zero value generated because the
-channel is closed and empty.
-</p>
-
-
-<h3 id="Conversions">Conversions</h3>
-
-<p>
-A conversion changes the <a href="#Types">type</a> of an expression
-to the type specified by the conversion.
-A conversion may appear literally in the source, or it may be <i>implied</i>
-by the context in which an expression appears.
-</p>
-
-<p>
-An <i>explicit</i> conversion is an expression of the form <code>T(x)</code>
-where <code>T</code> is a type and <code>x</code> is an expression
-that can be converted to type <code>T</code>.
-</p>
-
-<pre class="ebnf">
-Conversion = Type "(" Expression [ "," ] ")" .
-</pre>
-
-<p>
-If the type starts with the operator <code>*</code> or <code><-</code>,
-or if the type starts with the keyword <code>func</code>
-and has no result list, it must be parenthesized when
-necessary to avoid ambiguity:
-</p>
-
-<pre>
-*Point(p) // same as *(Point(p))
-(*Point)(p) // p is converted to *Point
-<-chan int(c) // same as <-(chan int(c))
-(<-chan int)(c) // c is converted to <-chan int
-func()(x) // function signature func() x
-(func())(x) // x is converted to func()
-(func() int)(x) // x is converted to func() int
-func() int(x) // x is converted to func() int (unambiguous)
-</pre>
-
-<p>
-A <a href="#Constants">constant</a> value <code>x</code> can be converted to
-type <code>T</code> if <code>x</code> is <a href="#Representability">representable</a>
-by a value of <code>T</code>.
-As a special case, an integer constant <code>x</code> can be explicitly converted to a
-<a href="#String_types">string type</a> using the
-<a href="#Conversions_to_and_from_a_string_type">same rule</a>
-as for non-constant <code>x</code>.
-</p>
-
-<p>
-Converting a constant yields a typed constant as result.
-</p>
-
-<pre>
-uint(iota) // iota value of type uint
-float32(2.718281828) // 2.718281828 of type float32
-complex128(1) // 1.0 + 0.0i of type complex128
-float32(0.49999999) // 0.5 of type float32
-float64(-1e-1000) // 0.0 of type float64
-string('x') // "x" of type string
-string(0x266c) // "♬" of type string
-MyString("foo" + "bar") // "foobar" of type MyString
-string([]byte{'a'}) // not a constant: []byte{'a'} is not a constant
-(*int)(nil) // not a constant: nil is not a constant, *int is not a boolean, numeric, or string type
-int(1.2) // illegal: 1.2 cannot be represented as an int
-string(65.0) // illegal: 65.0 is not an integer constant
-</pre>
-
-<p>
-A non-constant value <code>x</code> can be converted to type <code>T</code>
-in any of these cases:
-</p>
-
-<ul>
- <li>
- <code>x</code> is <a href="#Assignability">assignable</a>
- to <code>T</code>.
- </li>
- <li>
- ignoring struct tags (see below),
- <code>x</code>'s type and <code>T</code> have <a href="#Type_identity">identical</a>
- <a href="#Types">underlying types</a>.
- </li>
- <li>
- ignoring struct tags (see below),
- <code>x</code>'s type and <code>T</code> are pointer types
- that are not <a href="#Type_definitions">defined types</a>,
- and their pointer base types have identical underlying types.
- </li>
- <li>
- <code>x</code>'s type and <code>T</code> are both integer or floating
- point types.
- </li>
- <li>
- <code>x</code>'s type and <code>T</code> are both complex types.
- </li>
- <li>
- <code>x</code> is an integer or a slice of bytes or runes
- and <code>T</code> is a string type.
- </li>
- <li>
- <code>x</code> is a string and <code>T</code> is a slice of bytes or runes.
- </li>
- <li>
- <code>x</code> is a slice, <code>T</code> is a pointer to an array,
- and the slice and array types have <a href="#Type_identity">identical</a> element types.
- </li>
-</ul>
-
-<p>
-<a href="#Struct_types">Struct tags</a> are ignored when comparing struct types
-for identity for the purpose of conversion:
-</p>
-
-<pre>
-type Person struct {
- Name string
- Address *struct {
- Street string
- City string
- }
-}
-
-var data *struct {
- Name string `json:"name"`
- Address *struct {
- Street string `json:"street"`
- City string `json:"city"`
- } `json:"address"`
-}
-
-var person = (*Person)(data) // ignoring tags, the underlying types are identical
-</pre>
-
-<p>
-Specific rules apply to (non-constant) conversions between numeric types or
-to and from a string type.
-These conversions may change the representation of <code>x</code>
-and incur a run-time cost.
-All other conversions only change the type but not the representation
-of <code>x</code>.
-</p>
-
-<p>
-There is no linguistic mechanism to convert between pointers and integers.
-The package <a href="#Package_unsafe"><code>unsafe</code></a>
-implements this functionality under
-restricted circumstances.
-</p>
-
-<h4>Conversions between numeric types</h4>
-
-<p>
-For the conversion of non-constant numeric values, the following rules apply:
-</p>
-
-<ol>
-<li>
-When converting between integer types, if the value is a signed integer, it is
-sign extended to implicit infinite precision; otherwise it is zero extended.
-It is then truncated to fit in the result type's size.
-For example, if <code>v := uint16(0x10F0)</code>, then <code>uint32(int8(v)) == 0xFFFFFFF0</code>.
-The conversion always yields a valid value; there is no indication of overflow.
-</li>
-<li>
-When converting a floating-point number to an integer, the fraction is discarded
-(truncation towards zero).
-</li>
-<li>
-When converting an integer or floating-point number to a floating-point type,
-or a complex number to another complex type, the result value is rounded
-to the precision specified by the destination type.
-For instance, the value of a variable <code>x</code> of type <code>float32</code>
-may be stored using additional precision beyond that of an IEEE-754 32-bit number,
-but float32(x) represents the result of rounding <code>x</code>'s value to
-32-bit precision. Similarly, <code>x + 0.1</code> may use more than 32 bits
-of precision, but <code>float32(x + 0.1)</code> does not.
-</li>
-</ol>
-
-<p>
-In all non-constant conversions involving floating-point or complex values,
-if the result type cannot represent the value the conversion
-succeeds but the result value is implementation-dependent.
-</p>
-
-<h4 id="Conversions_to_and_from_a_string_type">Conversions to and from a string type</h4>
-
-<ol>
-<li>
-Converting a signed or unsigned integer value to a string type yields a
-string containing the UTF-8 representation of the integer. Values outside
-the range of valid Unicode code points are converted to <code>"\uFFFD"</code>.
-
-<pre>
-string('a') // "a"
-string(-1) // "\ufffd" == "\xef\xbf\xbd"
-string(0xf8) // "\u00f8" == "ø" == "\xc3\xb8"
-type MyString string
-MyString(0x65e5) // "\u65e5" == "日" == "\xe6\x97\xa5"
-</pre>
-</li>
-
-<li>
-Converting a slice of bytes to a string type yields
-a string whose successive bytes are the elements of the slice.
-
-<pre>
-string([]byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}) // "hellø"
-string([]byte{}) // ""
-string([]byte(nil)) // ""
-
-type MyBytes []byte
-string(MyBytes{'h', 'e', 'l', 'l', '\xc3', '\xb8'}) // "hellø"
-</pre>
-</li>
-
-<li>
-Converting a slice of runes to a string type yields
-a string that is the concatenation of the individual rune values
-converted to strings.
-
-<pre>
-string([]rune{0x767d, 0x9d6c, 0x7fd4}) // "\u767d\u9d6c\u7fd4" == "白鵬翔"
-string([]rune{}) // ""
-string([]rune(nil)) // ""
-
-type MyRunes []rune
-string(MyRunes{0x767d, 0x9d6c, 0x7fd4}) // "\u767d\u9d6c\u7fd4" == "白鵬翔"
-</pre>
-</li>
-
-<li>
-Converting a value of a string type to a slice of bytes type
-yields a slice whose successive elements are the bytes of the string.
-
-<pre>
-[]byte("hellø") // []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}
-[]byte("") // []byte{}
-
-MyBytes("hellø") // []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}
-</pre>
-</li>
-
-<li>
-Converting a value of a string type to a slice of runes type
-yields a slice containing the individual Unicode code points of the string.
-
-<pre>
-[]rune(MyString("白鵬翔")) // []rune{0x767d, 0x9d6c, 0x7fd4}
-[]rune("") // []rune{}
-
-MyRunes("白鵬翔") // []rune{0x767d, 0x9d6c, 0x7fd4}
-</pre>
-</li>
-</ol>
-
-<h4 id="Conversions_from_slice_to_array_pointer">Conversions from slice to array pointer</h4>
-
-<p>
-Converting a slice to an array pointer yields a pointer to the underlying array of the slice.
-If the <a href="#Length_and_capacity">length</a> of the slice is less than the length of the array,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<pre>
-s := make([]byte, 2, 4)
-s0 := (*[0]byte)(s) // s0 != nil
-s1 := (*[1]byte)(s[1:]) // &s1[0] == &s[1]
-s2 := (*[2]byte)(s) // &s2[0] == &s[0]
-s4 := (*[4]byte)(s) // panics: len([4]byte) > len(s)
-
-var t []string
-t0 := (*[0]string)(t) // t0 == nil
-t1 := (*[1]string)(t) // panics: len([1]string) > len(t)
-
-u := make([]byte, 0)
-u0 := (*[0]byte)(u) // u0 != nil
-</pre>
-
-<h3 id="Constant_expressions">Constant expressions</h3>
-
-<p>
-Constant expressions may contain only <a href="#Constants">constant</a>
-operands and are evaluated at compile time.
-</p>
-
-<p>
-Untyped boolean, numeric, and string constants may be used as operands
-wherever it is legal to use an operand of boolean, numeric, or string type,
-respectively.
-</p>
-
-<p>
-A constant <a href="#Comparison_operators">comparison</a> always yields
-an untyped boolean constant. If the left operand of a constant
-<a href="#Operators">shift expression</a> is an untyped constant, the
-result is an integer constant; otherwise it is a constant of the same
-type as the left operand, which must be of
-<a href="#Numeric_types">integer type</a>.
-</p>
-
-<p>
-Any other operation on untyped constants results in an untyped constant of the
-same kind; that is, a boolean, integer, floating-point, complex, or string
-constant.
-If the untyped operands of a binary operation (other than a shift) are of
-different kinds, the result is of the operand's kind that appears later in this
-list: integer, rune, floating-point, complex.
-For example, an untyped integer constant divided by an
-untyped complex constant yields an untyped complex constant.
-</p>
-
-<pre>
-const a = 2 + 3.0 // a == 5.0 (untyped floating-point constant)
-const b = 15 / 4 // b == 3 (untyped integer constant)
-const c = 15 / 4.0 // c == 3.75 (untyped floating-point constant)
-const Θ float64 = 3/2 // Θ == 1.0 (type float64, 3/2 is integer division)
-const Π float64 = 3/2. // Π == 1.5 (type float64, 3/2. is float division)
-const d = 1 << 3.0 // d == 8 (untyped integer constant)
-const e = 1.0 << 3 // e == 8 (untyped integer constant)
-const f = int32(1) << 33 // illegal (constant 8589934592 overflows int32)
-const g = float64(2) >> 1 // illegal (float64(2) is a typed floating-point constant)
-const h = "foo" > "bar" // h == true (untyped boolean constant)
-const j = true // j == true (untyped boolean constant)
-const k = 'w' + 1 // k == 'x' (untyped rune constant)
-const l = "hi" // l == "hi" (untyped string constant)
-const m = string(k) // m == "x" (type string)
-const Σ = 1 - 0.707i // (untyped complex constant)
-const Δ = Σ + 2.0e-4 // (untyped complex constant)
-const Φ = iota*1i - 1/1i // (untyped complex constant)
-</pre>
-
-<p>
-Applying the built-in function <code>complex</code> to untyped
-integer, rune, or floating-point constants yields
-an untyped complex constant.
-</p>
-
-<pre>
-const ic = complex(0, c) // ic == 3.75i (untyped complex constant)
-const iΘ = complex(0, Θ) // iΘ == 1i (type complex128)
-</pre>
-
-<p>
-Constant expressions are always evaluated exactly; intermediate values and the
-constants themselves may require precision significantly larger than supported
-by any predeclared type in the language. The following are legal declarations:
-</p>
-
-<pre>
-const Huge = 1 << 100 // Huge == 1267650600228229401496703205376 (untyped integer constant)
-const Four int8 = Huge >> 98 // Four == 4 (type int8)
-</pre>
-
-<p>
-The divisor of a constant division or remainder operation must not be zero:
-</p>
-
-<pre>
-3.14 / 0.0 // illegal: division by zero
-</pre>
-
-<p>
-The values of <i>typed</i> constants must always be accurately
-<a href="#Representability">representable</a> by values
-of the constant type. The following constant expressions are illegal:
-</p>
-
-<pre>
-uint(-1) // -1 cannot be represented as a uint
-int(3.14) // 3.14 cannot be represented as an int
-int64(Huge) // 1267650600228229401496703205376 cannot be represented as an int64
-Four * 300 // operand 300 cannot be represented as an int8 (type of Four)
-Four * 100 // product 400 cannot be represented as an int8 (type of Four)
-</pre>
-
-<p>
-The mask used by the unary bitwise complement operator <code>^</code> matches
-the rule for non-constants: the mask is all 1s for unsigned constants
-and -1 for signed and untyped constants.
-</p>
-
-<pre>
-^1 // untyped integer constant, equal to -2
-uint8(^1) // illegal: same as uint8(-2), -2 cannot be represented as a uint8
-^uint8(1) // typed uint8 constant, same as 0xFF ^ uint8(1) = uint8(0xFE)
-int8(^1) // same as int8(-2)
-^int8(1) // same as -1 ^ int8(1) = -2
-</pre>
-
-<p>
-Implementation restriction: A compiler may use rounding while
-computing untyped floating-point or complex constant expressions; see
-the implementation restriction in the section
-on <a href="#Constants">constants</a>. This rounding may cause a
-floating-point constant expression to be invalid in an integer
-context, even if it would be integral when calculated using infinite
-precision, and vice versa.
-</p>
-
-
-<h3 id="Order_of_evaluation">Order of evaluation</h3>
-
-<p>
-At package level, <a href="#Package_initialization">initialization dependencies</a>
-determine the evaluation order of individual initialization expressions in
-<a href="#Variable_declarations">variable declarations</a>.
-Otherwise, when evaluating the <a href="#Operands">operands</a> of an
-expression, assignment, or
-<a href="#Return_statements">return statement</a>,
-all function calls, method calls, and
-communication operations are evaluated in lexical left-to-right
-order.
-</p>
-
-<p>
-For example, in the (function-local) assignment
-</p>
-<pre>
-y[f()], ok = g(h(), i()+x[j()], <-c), k()
-</pre>
-<p>
-the function calls and communication happen in the order
-<code>f()</code>, <code>h()</code>, <code>i()</code>, <code>j()</code>,
-<code><-c</code>, <code>g()</code>, and <code>k()</code>.
-However, the order of those events compared to the evaluation
-and indexing of <code>x</code> and the evaluation
-of <code>y</code> is not specified.
-</p>
-
-<pre>
-a := 1
-f := func() int { a++; return a }
-x := []int{a, f()} // x may be [1, 2] or [2, 2]: evaluation order between a and f() is not specified
-m := map[int]int{a: 1, a: 2} // m may be {2: 1} or {2: 2}: evaluation order between the two map assignments is not specified
-n := map[int]int{a: f()} // n may be {2: 3} or {3: 3}: evaluation order between the key and the value is not specified
-</pre>
-
-<p>
-At package level, initialization dependencies override the left-to-right rule
-for individual initialization expressions, but not for operands within each
-expression:
-</p>
-
-<pre>
-var a, b, c = f() + v(), g(), sqr(u()) + v()
-
-func f() int { return c }
-func g() int { return a }
-func sqr(x int) int { return x*x }
-
-// functions u and v are independent of all other variables and functions
-</pre>
-
-<p>
-The function calls happen in the order
-<code>u()</code>, <code>sqr()</code>, <code>v()</code>,
-<code>f()</code>, <code>v()</code>, and <code>g()</code>.
-</p>
-
-<p>
-Floating-point operations within a single expression are evaluated according to
-the associativity of the operators. Explicit parentheses affect the evaluation
-by overriding the default associativity.
-In the expression <code>x + (y + z)</code> the addition <code>y + z</code>
-is performed before adding <code>x</code>.
-</p>
-
-<h2 id="Statements">Statements</h2>
-
-<p>
-Statements control execution.
-</p>
-
-<pre class="ebnf">
-Statement =
- Declaration | LabeledStmt | SimpleStmt |
- GoStmt | ReturnStmt | BreakStmt | ContinueStmt | GotoStmt |
- FallthroughStmt | Block | IfStmt | SwitchStmt | SelectStmt | ForStmt |
- DeferStmt .
-
-SimpleStmt = EmptyStmt | ExpressionStmt | SendStmt | IncDecStmt | Assignment | ShortVarDecl .
-</pre>
-
-<h3 id="Terminating_statements">Terminating statements</h3>
-
-<p>
-A <i>terminating statement</i> interrupts the regular flow of control in
-a <a href="#Blocks">block</a>. The following statements are terminating:
-</p>
-
-<ol>
-<li>
- A <a href="#Return_statements">"return"</a> or
- <a href="#Goto_statements">"goto"</a> statement.
- <!-- ul below only for regular layout -->
- <ul> </ul>
-</li>
-
-<li>
- A call to the built-in function
- <a href="#Handling_panics"><code>panic</code></a>.
- <!-- ul below only for regular layout -->
- <ul> </ul>
-</li>
-
-<li>
- A <a href="#Blocks">block</a> in which the statement list ends in a terminating statement.
- <!-- ul below only for regular layout -->
- <ul> </ul>
-</li>
-
-<li>
- An <a href="#If_statements">"if" statement</a> in which:
- <ul>
- <li>the "else" branch is present, and</li>
- <li>both branches are terminating statements.</li>
- </ul>
-</li>
-
-<li>
- A <a href="#For_statements">"for" statement</a> in which:
- <ul>
- <li>there are no "break" statements referring to the "for" statement, and</li>
- <li>the loop condition is absent, and</li>
- <li>the "for" statement does not use a range clause.</li>
- </ul>
-</li>
-
-<li>
- A <a href="#Switch_statements">"switch" statement</a> in which:
- <ul>
- <li>there are no "break" statements referring to the "switch" statement,</li>
- <li>there is a default case, and</li>
- <li>the statement lists in each case, including the default, end in a terminating
- statement, or a possibly labeled <a href="#Fallthrough_statements">"fallthrough"
- statement</a>.</li>
- </ul>
-</li>
-
-<li>
- A <a href="#Select_statements">"select" statement</a> in which:
- <ul>
- <li>there are no "break" statements referring to the "select" statement, and</li>
- <li>the statement lists in each case, including the default if present,
- end in a terminating statement.</li>
- </ul>
-</li>
-
-<li>
- A <a href="#Labeled_statements">labeled statement</a> labeling
- a terminating statement.
-</li>
-</ol>
-
-<p>
-All other statements are not terminating.
-</p>
-
-<p>
-A <a href="#Blocks">statement list</a> ends in a terminating statement if the list
-is not empty and its final non-empty statement is terminating.
-</p>
-
-
-<h3 id="Empty_statements">Empty statements</h3>
-
-<p>
-The empty statement does nothing.
-</p>
-
-<pre class="ebnf">
-EmptyStmt = .
-</pre>
-
-
-<h3 id="Labeled_statements">Labeled statements</h3>
-
-<p>
-A labeled statement may be the target of a <code>goto</code>,
-<code>break</code> or <code>continue</code> statement.
-</p>
-
-<pre class="ebnf">
-LabeledStmt = Label ":" Statement .
-Label = identifier .
-</pre>
-
-<pre>
-Error: log.Panic("error encountered")
-</pre>
-
-
-<h3 id="Expression_statements">Expression statements</h3>
-
-<p>
-With the exception of specific built-in functions,
-function and method <a href="#Calls">calls</a> and
-<a href="#Receive_operator">receive operations</a>
-can appear in statement context. Such statements may be parenthesized.
-</p>
-
-<pre class="ebnf">
-ExpressionStmt = Expression .
-</pre>
-
-<p>
-The following built-in functions are not permitted in statement context:
-</p>
-
-<pre>
-append cap complex imag len make new real
-unsafe.Add unsafe.Alignof unsafe.Offsetof unsafe.Sizeof unsafe.Slice
-</pre>
-
-<pre>
-h(x+y)
-f.Close()
-<-ch
-(<-ch)
-len("foo") // illegal if len is the built-in function
-</pre>
-
-
-<h3 id="Send_statements">Send statements</h3>
-
-<p>
-A send statement sends a value on a channel.
-The channel expression must be of <a href="#Channel_types">channel type</a>,
-the channel direction must permit send operations,
-and the type of the value to be sent must be <a href="#Assignability">assignable</a>
-to the channel's element type.
-</p>
-
-<pre class="ebnf">
-SendStmt = Channel "<-" Expression .
-Channel = Expression .
-</pre>
-
-<p>
-Both the channel and the value expression are evaluated before communication
-begins. Communication blocks until the send can proceed.
-A send on an unbuffered channel can proceed if a receiver is ready.
-A send on a buffered channel can proceed if there is room in the buffer.
-A send on a closed channel proceeds by causing a <a href="#Run_time_panics">run-time panic</a>.
-A send on a <code>nil</code> channel blocks forever.
-</p>
-
-<pre>
-ch <- 3 // send value 3 to channel ch
-</pre>
-
-
-<h3 id="IncDec_statements">IncDec statements</h3>
-
-<p>
-The "++" and "--" statements increment or decrement their operands
-by the untyped <a href="#Constants">constant</a> <code>1</code>.
-As with an assignment, the operand must be <a href="#Address_operators">addressable</a>
-or a map index expression.
-</p>
-
-<pre class="ebnf">
-IncDecStmt = Expression ( "++" | "--" ) .
-</pre>
-
-<p>
-The following <a href="#Assignments">assignment statements</a> are semantically
-equivalent:
-</p>
-
-<pre class="grammar">
-IncDec statement Assignment
-x++ x += 1
-x-- x -= 1
-</pre>
-
-
-<h3 id="Assignments">Assignments</h3>
-
-<pre class="ebnf">
-Assignment = ExpressionList assign_op ExpressionList .
-
-assign_op = [ add_op | mul_op ] "=" .
-</pre>
-
-<p>
-Each left-hand side operand must be <a href="#Address_operators">addressable</a>,
-a map index expression, or (for <code>=</code> assignments only) the
-<a href="#Blank_identifier">blank identifier</a>.
-Operands may be parenthesized.
-</p>
-
-<pre>
-x = 1
-*p = f()
-a[i] = 23
-(k) = <-ch // same as: k = <-ch
-</pre>
-
-<p>
-An <i>assignment operation</i> <code>x</code> <i>op</i><code>=</code>
-<code>y</code> where <i>op</i> is a binary <a href="#Arithmetic_operators">arithmetic operator</a>
-is equivalent to <code>x</code> <code>=</code> <code>x</code> <i>op</i>
-<code>(y)</code> but evaluates <code>x</code>
-only once. The <i>op</i><code>=</code> construct is a single token.
-In assignment operations, both the left- and right-hand expression lists
-must contain exactly one single-valued expression, and the left-hand
-expression must not be the blank identifier.
-</p>
-
-<pre>
-a[i] <<= 2
-i &^= 1<<n
-</pre>
-
-<p>
-A tuple assignment assigns the individual elements of a multi-valued
-operation to a list of variables. There are two forms. In the
-first, the right hand operand is a single multi-valued expression
-such as a function call, a <a href="#Channel_types">channel</a> or
-<a href="#Map_types">map</a> operation, or a <a href="#Type_assertions">type assertion</a>.
-The number of operands on the left
-hand side must match the number of values. For instance, if
-<code>f</code> is a function returning two values,
-</p>
-
-<pre>
-x, y = f()
-</pre>
-
-<p>
-assigns the first value to <code>x</code> and the second to <code>y</code>.
-In the second form, the number of operands on the left must equal the number
-of expressions on the right, each of which must be single-valued, and the
-<i>n</i>th expression on the right is assigned to the <i>n</i>th
-operand on the left:
-</p>
-
-<pre>
-one, two, three = '一', '二', '三'
-</pre>
-
-<p>
-The <a href="#Blank_identifier">blank identifier</a> provides a way to
-ignore right-hand side values in an assignment:
-</p>
-
-<pre>
-_ = x // evaluate x but ignore it
-x, _ = f() // evaluate f() but ignore second result value
-</pre>
-
-<p>
-The assignment proceeds in two phases.
-First, the operands of <a href="#Index_expressions">index expressions</a>
-and <a href="#Address_operators">pointer indirections</a>
-(including implicit pointer indirections in <a href="#Selectors">selectors</a>)
-on the left and the expressions on the right are all
-<a href="#Order_of_evaluation">evaluated in the usual order</a>.
-Second, the assignments are carried out in left-to-right order.
-</p>
-
-<pre>
-a, b = b, a // exchange a and b
-
-x := []int{1, 2, 3}
-i := 0
-i, x[i] = 1, 2 // set i = 1, x[0] = 2
-
-i = 0
-x[i], i = 2, 1 // set x[0] = 2, i = 1
-
-x[0], x[0] = 1, 2 // set x[0] = 1, then x[0] = 2 (so x[0] == 2 at end)
-
-x[1], x[3] = 4, 5 // set x[1] = 4, then panic setting x[3] = 5.
-
-type Point struct { x, y int }
-var p *Point
-x[2], p.x = 6, 7 // set x[2] = 6, then panic setting p.x = 7
-
-i = 2
-x = []int{3, 5, 7}
-for i, x[i] = range x { // set i, x[2] = 0, x[0]
- break
-}
-// after this loop, i == 0 and x == []int{3, 5, 3}
-</pre>
-
-<p>
-In assignments, each value must be <a href="#Assignability">assignable</a>
-to the type of the operand to which it is assigned, with the following special cases:
-</p>
-
-<ol>
-<li>
- Any typed value may be assigned to the blank identifier.
-</li>
-
-<li>
- If an untyped constant
- is assigned to a variable of interface type or the blank identifier,
- the constant is first implicitly <a href="#Conversions">converted</a> to its
- <a href="#Constants">default type</a>.
-</li>
-
-<li>
- If an untyped boolean value is assigned to a variable of interface type or
- the blank identifier, it is first implicitly converted to type <code>bool</code>.
-</li>
-</ol>
-
-<h3 id="If_statements">If statements</h3>
-
-<p>
-"If" statements specify the conditional execution of two branches
-according to the value of a boolean expression. If the expression
-evaluates to true, the "if" branch is executed, otherwise, if
-present, the "else" branch is executed.
-</p>
-
-<pre class="ebnf">
-IfStmt = "if" [ SimpleStmt ";" ] Expression Block [ "else" ( IfStmt | Block ) ] .
-</pre>
-
-<pre>
-if x > max {
- x = max
-}
-</pre>
-
-<p>
-The expression may be preceded by a simple statement, which
-executes before the expression is evaluated.
-</p>
-
-<pre>
-if x := f(); x < y {
- return x
-} else if x > z {
- return z
-} else {
- return y
-}
-</pre>
-
-
-<h3 id="Switch_statements">Switch statements</h3>
-
-<p>
-"Switch" statements provide multi-way execution.
-An expression or type is compared to the "cases"
-inside the "switch" to determine which branch
-to execute.
-</p>
-
-<pre class="ebnf">
-SwitchStmt = ExprSwitchStmt | TypeSwitchStmt .
-</pre>
-
-<p>
-There are two forms: expression switches and type switches.
-In an expression switch, the cases contain expressions that are compared
-against the value of the switch expression.
-In a type switch, the cases contain types that are compared against the
-type of a specially annotated switch expression.
-The switch expression is evaluated exactly once in a switch statement.
-</p>
-
-<h4 id="Expression_switches">Expression switches</h4>
-
-<p>
-In an expression switch,
-the switch expression is evaluated and
-the case expressions, which need not be constants,
-are evaluated left-to-right and top-to-bottom; the first one that equals the
-switch expression
-triggers execution of the statements of the associated case;
-the other cases are skipped.
-If no case matches and there is a "default" case,
-its statements are executed.
-There can be at most one default case and it may appear anywhere in the
-"switch" statement.
-A missing switch expression is equivalent to the boolean value
-<code>true</code>.
-</p>
-
-<pre class="ebnf">
-ExprSwitchStmt = "switch" [ SimpleStmt ";" ] [ Expression ] "{" { ExprCaseClause } "}" .
-ExprCaseClause = ExprSwitchCase ":" StatementList .
-ExprSwitchCase = "case" ExpressionList | "default" .
-</pre>
-
-<p>
-If the switch expression evaluates to an untyped constant, it is first implicitly
-<a href="#Conversions">converted</a> to its <a href="#Constants">default type</a>.
-The predeclared untyped value <code>nil</code> cannot be used as a switch expression.
-The switch expression type must be <a href="#Comparison_operators">comparable</a>.
-</p>
-
-<p>
-If a case expression is untyped, it is first implicitly <a href="#Conversions">converted</a>
-to the type of the switch expression.
-For each (possibly converted) case expression <code>x</code> and the value <code>t</code>
-of the switch expression, <code>x == t</code> must be a valid <a href="#Comparison_operators">comparison</a>.
-</p>
-
-<p>
-In other words, the switch expression is treated as if it were used to declare and
-initialize a temporary variable <code>t</code> without explicit type; it is that
-value of <code>t</code> against which each case expression <code>x</code> is tested
-for equality.
-</p>
-
-<p>
-In a case or default clause, the last non-empty statement
-may be a (possibly <a href="#Labeled_statements">labeled</a>)
-<a href="#Fallthrough_statements">"fallthrough" statement</a> to
-indicate that control should flow from the end of this clause to
-the first statement of the next clause.
-Otherwise control flows to the end of the "switch" statement.
-A "fallthrough" statement may appear as the last statement of all
-but the last clause of an expression switch.
-</p>
-
-<p>
-The switch expression may be preceded by a simple statement, which
-executes before the expression is evaluated.
-</p>
-
-<pre>
-switch tag {
-default: s3()
-case 0, 1, 2, 3: s1()
-case 4, 5, 6, 7: s2()
-}
-
-switch x := f(); { // missing switch expression means "true"
-case x < 0: return -x
-default: return x
-}
-
-switch {
-case x < y: f1()
-case x < z: f2()
-case x == 4: f3()
-}
-</pre>
-
-<p>
-Implementation restriction: A compiler may disallow multiple case
-expressions evaluating to the same constant.
-For instance, the current compilers disallow duplicate integer,
-floating point, or string constants in case expressions.
-</p>
-
-<h4 id="Type_switches">Type switches</h4>
-
-<p>
-A type switch compares types rather than values. It is otherwise similar
-to an expression switch. It is marked by a special switch expression that
-has the form of a <a href="#Type_assertions">type assertion</a>
-using the keyword <code>type</code> rather than an actual type:
-</p>
-
-<pre>
-switch x.(type) {
-// cases
-}
-</pre>
-
-<p>
-Cases then match actual types <code>T</code> against the dynamic type of the
-expression <code>x</code>. As with type assertions, <code>x</code> must be of
-<a href="#Interface_types">interface type</a>, and each non-interface type
-<code>T</code> listed in a case must implement the type of <code>x</code>.
-The types listed in the cases of a type switch must all be
-<a href="#Type_identity">different</a>.
-</p>
-
-<pre class="ebnf">
-TypeSwitchStmt = "switch" [ SimpleStmt ";" ] TypeSwitchGuard "{" { TypeCaseClause } "}" .
-TypeSwitchGuard = [ identifier ":=" ] PrimaryExpr "." "(" "type" ")" .
-TypeCaseClause = TypeSwitchCase ":" StatementList .
-TypeSwitchCase = "case" TypeList | "default" .
-TypeList = Type { "," Type } .
-</pre>
-
-<p>
-The TypeSwitchGuard may include a
-<a href="#Short_variable_declarations">short variable declaration</a>.
-When that form is used, the variable is declared at the end of the
-TypeSwitchCase in the <a href="#Blocks">implicit block</a> of each clause.
-In clauses with a case listing exactly one type, the variable
-has that type; otherwise, the variable has the type of the expression
-in the TypeSwitchGuard.
-</p>
-
-<p>
-Instead of a type, a case may use the predeclared identifier
-<a href="#Predeclared_identifiers"><code>nil</code></a>;
-that case is selected when the expression in the TypeSwitchGuard
-is a <code>nil</code> interface value.
-There may be at most one <code>nil</code> case.
-</p>
-
-<p>
-Given an expression <code>x</code> of type <code>interface{}</code>,
-the following type switch:
-</p>
-
-<pre>
-switch i := x.(type) {
-case nil:
- printString("x is nil") // type of i is type of x (interface{})
-case int:
- printInt(i) // type of i is int
-case float64:
- printFloat64(i) // type of i is float64
-case func(int) float64:
- printFunction(i) // type of i is func(int) float64
-case bool, string:
- printString("type is bool or string") // type of i is type of x (interface{})
-default:
- printString("don't know the type") // type of i is type of x (interface{})
-}
-</pre>
-
-<p>
-could be rewritten:
-</p>
-
-<pre>
-v := x // x is evaluated exactly once
-if v == nil {
- i := v // type of i is type of x (interface{})
- printString("x is nil")
-} else if i, isInt := v.(int); isInt {
- printInt(i) // type of i is int
-} else if i, isFloat64 := v.(float64); isFloat64 {
- printFloat64(i) // type of i is float64
-} else if i, isFunc := v.(func(int) float64); isFunc {
- printFunction(i) // type of i is func(int) float64
-} else {
- _, isBool := v.(bool)
- _, isString := v.(string)
- if isBool || isString {
- i := v // type of i is type of x (interface{})
- printString("type is bool or string")
- } else {
- i := v // type of i is type of x (interface{})
- printString("don't know the type")
- }
-}
-</pre>
-
-<p>
-The type switch guard may be preceded by a simple statement, which
-executes before the guard is evaluated.
-</p>
-
-<p>
-The "fallthrough" statement is not permitted in a type switch.
-</p>
-
-<h3 id="For_statements">For statements</h3>
-
-<p>
-A "for" statement specifies repeated execution of a block. There are three forms:
-The iteration may be controlled by a single condition, a "for" clause, or a "range" clause.
-</p>
-
-<pre class="ebnf">
-ForStmt = "for" [ Condition | ForClause | RangeClause ] Block .
-Condition = Expression .
-</pre>
-
-<h4 id="For_condition">For statements with single condition</h4>
-
-<p>
-In its simplest form, a "for" statement specifies the repeated execution of
-a block as long as a boolean condition evaluates to true.
-The condition is evaluated before each iteration.
-If the condition is absent, it is equivalent to the boolean value
-<code>true</code>.
-</p>
-
-<pre>
-for a < b {
- a *= 2
-}
-</pre>
-
-<h4 id="For_clause">For statements with <code>for</code> clause</h4>
-
-<p>
-A "for" statement with a ForClause is also controlled by its condition, but
-additionally it may specify an <i>init</i>
-and a <i>post</i> statement, such as an assignment,
-an increment or decrement statement. The init statement may be a
-<a href="#Short_variable_declarations">short variable declaration</a>, but the post statement must not.
-Variables declared by the init statement are re-used in each iteration.
-</p>
-
-<pre class="ebnf">
-ForClause = [ InitStmt ] ";" [ Condition ] ";" [ PostStmt ] .
-InitStmt = SimpleStmt .
-PostStmt = SimpleStmt .
-</pre>
-
-<pre>
-for i := 0; i < 10; i++ {
- f(i)
-}
-</pre>
-
-<p>
-If non-empty, the init statement is executed once before evaluating the
-condition for the first iteration;
-the post statement is executed after each execution of the block (and
-only if the block was executed).
-Any element of the ForClause may be empty but the
-<a href="#Semicolons">semicolons</a> are
-required unless there is only a condition.
-If the condition is absent, it is equivalent to the boolean value
-<code>true</code>.
-</p>
-
-<pre>
-for cond { S() } is the same as for ; cond ; { S() }
-for { S() } is the same as for true { S() }
-</pre>
-
-<h4 id="For_range">For statements with <code>range</code> clause</h4>
-
-<p>
-A "for" statement with a "range" clause
-iterates through all entries of an array, slice, string or map,
-or values received on a channel. For each entry it assigns <i>iteration values</i>
-to corresponding <i>iteration variables</i> if present and then executes the block.
-</p>
-
-<pre class="ebnf">
-RangeClause = [ ExpressionList "=" | IdentifierList ":=" ] "range" Expression .
-</pre>
-
-<p>
-The expression on the right in the "range" clause is called the <i>range expression</i>,
-which may be an array, pointer to an array, slice, string, map, or channel permitting
-<a href="#Receive_operator">receive operations</a>.
-As with an assignment, if present the operands on the left must be
-<a href="#Address_operators">addressable</a> or map index expressions; they
-denote the iteration variables. If the range expression is a channel, at most
-one iteration variable is permitted, otherwise there may be up to two.
-If the last iteration variable is the <a href="#Blank_identifier">blank identifier</a>,
-the range clause is equivalent to the same clause without that identifier.
-</p>
-
-<p>
-The range expression <code>x</code> is evaluated once before beginning the loop,
-with one exception: if at most one iteration variable is present and
-<code>len(x)</code> is <a href="#Length_and_capacity">constant</a>,
-the range expression is not evaluated.
-</p>
-
-<p>
-Function calls on the left are evaluated once per iteration.
-For each iteration, iteration values are produced as follows
-if the respective iteration variables are present:
-</p>
-
-<pre class="grammar">
-Range expression 1st value 2nd value
-
-array or slice a [n]E, *[n]E, or []E index i int a[i] E
-string s string type index i int see below rune
-map m map[K]V key k K m[k] V
-channel c chan E, <-chan E element e E
-</pre>
-
-<ol>
-<li>
-For an array, pointer to array, or slice value <code>a</code>, the index iteration
-values are produced in increasing order, starting at element index 0.
-If at most one iteration variable is present, the range loop produces
-iteration values from 0 up to <code>len(a)-1</code> and does not index into the array
-or slice itself. For a <code>nil</code> slice, the number of iterations is 0.
-</li>
-
-<li>
-For a string value, the "range" clause iterates over the Unicode code points
-in the string starting at byte index 0. On successive iterations, the index value will be the
-index of the first byte of successive UTF-8-encoded code points in the string,
-and the second value, of type <code>rune</code>, will be the value of
-the corresponding code point. If the iteration encounters an invalid
-UTF-8 sequence, the second value will be <code>0xFFFD</code>,
-the Unicode replacement character, and the next iteration will advance
-a single byte in the string.
-</li>
-
-<li>
-The iteration order over maps is not specified
-and is not guaranteed to be the same from one iteration to the next.
-If a map entry that has not yet been reached is removed during iteration,
-the corresponding iteration value will not be produced. If a map entry is
-created during iteration, that entry may be produced during the iteration or
-may be skipped. The choice may vary for each entry created and from one
-iteration to the next.
-If the map is <code>nil</code>, the number of iterations is 0.
-</li>
-
-<li>
-For channels, the iteration values produced are the successive values sent on
-the channel until the channel is <a href="#Close">closed</a>. If the channel
-is <code>nil</code>, the range expression blocks forever.
-</li>
-</ol>
-
-<p>
-The iteration values are assigned to the respective
-iteration variables as in an <a href="#Assignments">assignment statement</a>.
-</p>
-
-<p>
-The iteration variables may be declared by the "range" clause using a form of
-<a href="#Short_variable_declarations">short variable declaration</a>
-(<code>:=</code>).
-In this case their types are set to the types of the respective iteration values
-and their <a href="#Declarations_and_scope">scope</a> is the block of the "for"
-statement; they are re-used in each iteration.
-If the iteration variables are declared outside the "for" statement,
-after execution their values will be those of the last iteration.
-</p>
-
-<pre>
-var testdata *struct {
- a *[7]int
-}
-for i, _ := range testdata.a {
- // testdata.a is never evaluated; len(testdata.a) is constant
- // i ranges from 0 to 6
- f(i)
-}
-
-var a [10]string
-for i, s := range a {
- // type of i is int
- // type of s is string
- // s == a[i]
- g(i, s)
-}
-
-var key string
-var val interface{} // element type of m is assignable to val
-m := map[string]int{"mon":0, "tue":1, "wed":2, "thu":3, "fri":4, "sat":5, "sun":6}
-for key, val = range m {
- h(key, val)
-}
-// key == last map key encountered in iteration
-// val == map[key]
-
-var ch chan Work = producer()
-for w := range ch {
- doWork(w)
-}
-
-// empty a channel
-for range ch {}
-</pre>
-
-
-<h3 id="Go_statements">Go statements</h3>
-
-<p>
-A "go" statement starts the execution of a function call
-as an independent concurrent thread of control, or <i>goroutine</i>,
-within the same address space.
-</p>
-
-<pre class="ebnf">
-GoStmt = "go" Expression .
-</pre>
-
-<p>
-The expression must be a function or method call; it cannot be parenthesized.
-Calls of built-in functions are restricted as for
-<a href="#Expression_statements">expression statements</a>.
-</p>
-
-<p>
-The function value and parameters are
-<a href="#Calls">evaluated as usual</a>
-in the calling goroutine, but
-unlike with a regular call, program execution does not wait
-for the invoked function to complete.
-Instead, the function begins executing independently
-in a new goroutine.
-When the function terminates, its goroutine also terminates.
-If the function has any return values, they are discarded when the
-function completes.
-</p>
-
-<pre>
-go Server()
-go func(ch chan<- bool) { for { sleep(10); ch <- true }} (c)
-</pre>
-
-
-<h3 id="Select_statements">Select statements</h3>
-
-<p>
-A "select" statement chooses which of a set of possible
-<a href="#Send_statements">send</a> or
-<a href="#Receive_operator">receive</a>
-operations will proceed.
-It looks similar to a
-<a href="#Switch_statements">"switch"</a> statement but with the
-cases all referring to communication operations.
-</p>
-
-<pre class="ebnf">
-SelectStmt = "select" "{" { CommClause } "}" .
-CommClause = CommCase ":" StatementList .
-CommCase = "case" ( SendStmt | RecvStmt ) | "default" .
-RecvStmt = [ ExpressionList "=" | IdentifierList ":=" ] RecvExpr .
-RecvExpr = Expression .
-</pre>
-
-<p>
-A case with a RecvStmt may assign the result of a RecvExpr to one or
-two variables, which may be declared using a
-<a href="#Short_variable_declarations">short variable declaration</a>.
-The RecvExpr must be a (possibly parenthesized) receive operation.
-There can be at most one default case and it may appear anywhere
-in the list of cases.
-</p>
-
-<p>
-Execution of a "select" statement proceeds in several steps:
-</p>
-
-<ol>
-<li>
-For all the cases in the statement, the channel operands of receive operations
-and the channel and right-hand-side expressions of send statements are
-evaluated exactly once, in source order, upon entering the "select" statement.
-The result is a set of channels to receive from or send to,
-and the corresponding values to send.
-Any side effects in that evaluation will occur irrespective of which (if any)
-communication operation is selected to proceed.
-Expressions on the left-hand side of a RecvStmt with a short variable declaration
-or assignment are not yet evaluated.
-</li>
-
-<li>
-If one or more of the communications can proceed,
-a single one that can proceed is chosen via a uniform pseudo-random selection.
-Otherwise, if there is a default case, that case is chosen.
-If there is no default case, the "select" statement blocks until
-at least one of the communications can proceed.
-</li>
-
-<li>
-Unless the selected case is the default case, the respective communication
-operation is executed.
-</li>
-
-<li>
-If the selected case is a RecvStmt with a short variable declaration or
-an assignment, the left-hand side expressions are evaluated and the
-received value (or values) are assigned.
-</li>
-
-<li>
-The statement list of the selected case is executed.
-</li>
-</ol>
-
-<p>
-Since communication on <code>nil</code> channels can never proceed,
-a select with only <code>nil</code> channels and no default case blocks forever.
-</p>
-
-<pre>
-var a []int
-var c, c1, c2, c3, c4 chan int
-var i1, i2 int
-select {
-case i1 = <-c1:
- print("received ", i1, " from c1\n")
-case c2 <- i2:
- print("sent ", i2, " to c2\n")
-case i3, ok := (<-c3): // same as: i3, ok := <-c3
- if ok {
- print("received ", i3, " from c3\n")
- } else {
- print("c3 is closed\n")
- }
-case a[f()] = <-c4:
- // same as:
- // case t := <-c4
- // a[f()] = t
-default:
- print("no communication\n")
-}
-
-for { // send random sequence of bits to c
- select {
- case c <- 0: // note: no statement, no fallthrough, no folding of cases
- case c <- 1:
- }
-}
-
-select {} // block forever
-</pre>
-
-
-<h3 id="Return_statements">Return statements</h3>
-
-<p>
-A "return" statement in a function <code>F</code> terminates the execution
-of <code>F</code>, and optionally provides one or more result values.
-Any functions <a href="#Defer_statements">deferred</a> by <code>F</code>
-are executed before <code>F</code> returns to its caller.
-</p>
-
-<pre class="ebnf">
-ReturnStmt = "return" [ ExpressionList ] .
-</pre>
-
-<p>
-In a function without a result type, a "return" statement must not
-specify any result values.
-</p>
-<pre>
-func noResult() {
- return
-}
-</pre>
-
-<p>
-There are three ways to return values from a function with a result
-type:
-</p>
-
-<ol>
- <li>The return value or values may be explicitly listed
- in the "return" statement. Each expression must be single-valued
- and <a href="#Assignability">assignable</a>
- to the corresponding element of the function's result type.
-<pre>
-func simpleF() int {
- return 2
-}
-
-func complexF1() (re float64, im float64) {
- return -7.0, -4.0
-}
-</pre>
- </li>
- <li>The expression list in the "return" statement may be a single
- call to a multi-valued function. The effect is as if each value
- returned from that function were assigned to a temporary
- variable with the type of the respective value, followed by a
- "return" statement listing these variables, at which point the
- rules of the previous case apply.
-<pre>
-func complexF2() (re float64, im float64) {
- return complexF1()
-}
-</pre>
- </li>
- <li>The expression list may be empty if the function's result
- type specifies names for its <a href="#Function_types">result parameters</a>.
- The result parameters act as ordinary local variables
- and the function may assign values to them as necessary.
- The "return" statement returns the values of these variables.
-<pre>
-func complexF3() (re float64, im float64) {
- re = 7.0
- im = 4.0
- return
-}
-
-func (devnull) Write(p []byte) (n int, _ error) {
- n = len(p)
- return
-}
-</pre>
- </li>
-</ol>
-
-<p>
-Regardless of how they are declared, all the result values are initialized to
-the <a href="#The_zero_value">zero values</a> for their type upon entry to the
-function. A "return" statement that specifies results sets the result parameters before
-any deferred functions are executed.
-</p>
-
-<p>
-Implementation restriction: A compiler may disallow an empty expression list
-in a "return" statement if a different entity (constant, type, or variable)
-with the same name as a result parameter is in
-<a href="#Declarations_and_scope">scope</a> at the place of the return.
-</p>
-
-<pre>
-func f(n int) (res int, err error) {
- if _, err := f(n-1); err != nil {
- return // invalid return statement: err is shadowed
- }
- return
-}
-</pre>
-
-<h3 id="Break_statements">Break statements</h3>
-
-<p>
-A "break" statement terminates execution of the innermost
-<a href="#For_statements">"for"</a>,
-<a href="#Switch_statements">"switch"</a>, or
-<a href="#Select_statements">"select"</a> statement
-within the same function.
-</p>
-
-<pre class="ebnf">
-BreakStmt = "break" [ Label ] .
-</pre>
-
-<p>
-If there is a label, it must be that of an enclosing
-"for", "switch", or "select" statement,
-and that is the one whose execution terminates.
-</p>
-
-<pre>
-OuterLoop:
- for i = 0; i < n; i++ {
- for j = 0; j < m; j++ {
- switch a[i][j] {
- case nil:
- state = Error
- break OuterLoop
- case item:
- state = Found
- break OuterLoop
- }
- }
- }
-</pre>
-
-<h3 id="Continue_statements">Continue statements</h3>
-
-<p>
-A "continue" statement begins the next iteration of the
-innermost <a href="#For_statements">"for" loop</a> at its post statement.
-The "for" loop must be within the same function.
-</p>
-
-<pre class="ebnf">
-ContinueStmt = "continue" [ Label ] .
-</pre>
-
-<p>
-If there is a label, it must be that of an enclosing
-"for" statement, and that is the one whose execution
-advances.
-</p>
-
-<pre>
-RowLoop:
- for y, row := range rows {
- for x, data := range row {
- if data == endOfRow {
- continue RowLoop
- }
- row[x] = data + bias(x, y)
- }
- }
-</pre>
-
-<h3 id="Goto_statements">Goto statements</h3>
-
-<p>
-A "goto" statement transfers control to the statement with the corresponding label
-within the same function.
-</p>
-
-<pre class="ebnf">
-GotoStmt = "goto" Label .
-</pre>
-
-<pre>
-goto Error
-</pre>
-
-<p>
-Executing the "goto" statement must not cause any variables to come into
-<a href="#Declarations_and_scope">scope</a> that were not already in scope at the point of the goto.
-For instance, this example:
-</p>
-
-<pre>
- goto L // BAD
- v := 3
-L:
-</pre>
-
-<p>
-is erroneous because the jump to label <code>L</code> skips
-the creation of <code>v</code>.
-</p>
-
-<p>
-A "goto" statement outside a <a href="#Blocks">block</a> cannot jump to a label inside that block.
-For instance, this example:
-</p>
-
-<pre>
-if n%2 == 1 {
- goto L1
-}
-for n > 0 {
- f()
- n--
-L1:
- f()
- n--
-}
-</pre>
-
-<p>
-is erroneous because the label <code>L1</code> is inside
-the "for" statement's block but the <code>goto</code> is not.
-</p>
-
-<h3 id="Fallthrough_statements">Fallthrough statements</h3>
-
-<p>
-A "fallthrough" statement transfers control to the first statement of the
-next case clause in an <a href="#Expression_switches">expression "switch" statement</a>.
-It may be used only as the final non-empty statement in such a clause.
-</p>
-
-<pre class="ebnf">
-FallthroughStmt = "fallthrough" .
-</pre>
-
-
-<h3 id="Defer_statements">Defer statements</h3>
-
-<p>
-A "defer" statement invokes a function whose execution is deferred
-to the moment the surrounding function returns, either because the
-surrounding function executed a <a href="#Return_statements">return statement</a>,
-reached the end of its <a href="#Function_declarations">function body</a>,
-or because the corresponding goroutine is <a href="#Handling_panics">panicking</a>.
-</p>
-
-<pre class="ebnf">
-DeferStmt = "defer" Expression .
-</pre>
-
-<p>
-The expression must be a function or method call; it cannot be parenthesized.
-Calls of built-in functions are restricted as for
-<a href="#Expression_statements">expression statements</a>.
-</p>
-
-<p>
-Each time a "defer" statement
-executes, the function value and parameters to the call are
-<a href="#Calls">evaluated as usual</a>
-and saved anew but the actual function is not invoked.
-Instead, deferred functions are invoked immediately before
-the surrounding function returns, in the reverse order
-they were deferred. That is, if the surrounding function
-returns through an explicit <a href="#Return_statements">return statement</a>,
-deferred functions are executed <i>after</i> any result parameters are set
-by that return statement but <i>before</i> the function returns to its caller.
-If a deferred function value evaluates
-to <code>nil</code>, execution <a href="#Handling_panics">panics</a>
-when the function is invoked, not when the "defer" statement is executed.
-</p>
-
-<p>
-For instance, if the deferred function is
-a <a href="#Function_literals">function literal</a> and the surrounding
-function has <a href="#Function_types">named result parameters</a> that
-are in scope within the literal, the deferred function may access and modify
-the result parameters before they are returned.
-If the deferred function has any return values, they are discarded when
-the function completes.
-(See also the section on <a href="#Handling_panics">handling panics</a>.)
-</p>
-
-<pre>
-lock(l)
-defer unlock(l) // unlocking happens before surrounding function returns
-
-// prints 3 2 1 0 before surrounding function returns
-for i := 0; i <= 3; i++ {
- defer fmt.Print(i)
-}
-
-// f returns 42
-func f() (result int) {
- defer func() {
- // result is accessed after it was set to 6 by the return statement
- result *= 7
- }()
- return 6
-}
-</pre>
-
-<h2 id="Built-in_functions">Built-in functions</h2>
-
-<p>
-Built-in functions are
-<a href="#Predeclared_identifiers">predeclared</a>.
-They are called like any other function but some of them
-accept a type instead of an expression as the first argument.
-</p>
-
-<p>
-The built-in functions do not have standard Go types,
-so they can only appear in <a href="#Calls">call expressions</a>;
-they cannot be used as function values.
-</p>
-
-<h3 id="Close">Close</h3>
-
-<p>
-For a channel <code>c</code>, the built-in function <code>close(c)</code>
-records that no more values will be sent on the channel.
-It is an error if <code>c</code> is a receive-only channel.
-Sending to or closing a closed channel causes a <a href="#Run_time_panics">run-time panic</a>.
-Closing the nil channel also causes a <a href="#Run_time_panics">run-time panic</a>.
-After calling <code>close</code>, and after any previously
-sent values have been received, receive operations will return
-the zero value for the channel's type without blocking.
-The multi-valued <a href="#Receive_operator">receive operation</a>
-returns a received value along with an indication of whether the channel is closed.
-</p>
-
-
-<h3 id="Length_and_capacity">Length and capacity</h3>
-
-<p>
-The built-in functions <code>len</code> and <code>cap</code> take arguments
-of various types and return a result of type <code>int</code>.
-The implementation guarantees that the result always fits into an <code>int</code>.
-</p>
-
-<pre class="grammar">
-Call Argument type Result
-
-len(s) string type string length in bytes
- [n]T, *[n]T array length (== n)
- []T slice length
- map[K]T map length (number of defined keys)
- chan T number of elements queued in channel buffer
-
-cap(s) [n]T, *[n]T array length (== n)
- []T slice capacity
- chan T channel buffer capacity
-</pre>
-
-<p>
-The capacity of a slice is the number of elements for which there is
-space allocated in the underlying array.
-At any time the following relationship holds:
-</p>
-
-<pre>
-0 <= len(s) <= cap(s)
-</pre>
-
-<p>
-The length of a <code>nil</code> slice, map or channel is 0.
-The capacity of a <code>nil</code> slice or channel is 0.
-</p>
-
-<p>
-The expression <code>len(s)</code> is <a href="#Constants">constant</a> if
-<code>s</code> is a string constant. The expressions <code>len(s)</code> and
-<code>cap(s)</code> are constants if the type of <code>s</code> is an array
-or pointer to an array and the expression <code>s</code> does not contain
-<a href="#Receive_operator">channel receives</a> or (non-constant)
-<a href="#Calls">function calls</a>; in this case <code>s</code> is not evaluated.
-Otherwise, invocations of <code>len</code> and <code>cap</code> are not
-constant and <code>s</code> is evaluated.
-</p>
-
-<pre>
-const (
- c1 = imag(2i) // imag(2i) = 2.0 is a constant
- c2 = len([10]float64{2}) // [10]float64{2} contains no function calls
- c3 = len([10]float64{c1}) // [10]float64{c1} contains no function calls
- c4 = len([10]float64{imag(2i)}) // imag(2i) is a constant and no function call is issued
- c5 = len([10]float64{imag(z)}) // invalid: imag(z) is a (non-constant) function call
-)
-var z complex128
-</pre>
-
-<h3 id="Allocation">Allocation</h3>
-
-<p>
-The built-in function <code>new</code> takes a type <code>T</code>,
-allocates storage for a <a href="#Variables">variable</a> of that type
-at run time, and returns a value of type <code>*T</code>
-<a href="#Pointer_types">pointing</a> to it.
-The variable is initialized as described in the section on
-<a href="#The_zero_value">initial values</a>.
-</p>
-
-<pre class="grammar">
-new(T)
-</pre>
-
-<p>
-For instance
-</p>
-
-<pre>
-type S struct { a int; b float64 }
-new(S)
-</pre>
-
-<p>
-allocates storage for a variable of type <code>S</code>,
-initializes it (<code>a=0</code>, <code>b=0.0</code>),
-and returns a value of type <code>*S</code> containing the address
-of the location.
-</p>
-
-<h3 id="Making_slices_maps_and_channels">Making slices, maps and channels</h3>
-
-<p>
-The built-in function <code>make</code> takes a type <code>T</code>,
-which must be a slice, map or channel type,
-optionally followed by a type-specific list of expressions.
-It returns a value of type <code>T</code> (not <code>*T</code>).
-The memory is initialized as described in the section on
-<a href="#The_zero_value">initial values</a>.
-</p>
-
-<pre class="grammar">
-Call Type T Result
-
-make(T, n) slice slice of type T with length n and capacity n
-make(T, n, m) slice slice of type T with length n and capacity m
-
-make(T) map map of type T
-make(T, n) map map of type T with initial space for approximately n elements
-
-make(T) channel unbuffered channel of type T
-make(T, n) channel buffered channel of type T, buffer size n
-</pre>
-
-
-<p>
-Each of the size arguments <code>n</code> and <code>m</code> must be of integer type
-or an untyped <a href="#Constants">constant</a>.
-A constant size argument must be non-negative and <a href="#Representability">representable</a>
-by a value of type <code>int</code>; if it is an untyped constant it is given type <code>int</code>.
-If both <code>n</code> and <code>m</code> are provided and are constant, then
-<code>n</code> must be no larger than <code>m</code>.
-If <code>n</code> is negative or larger than <code>m</code> at run time,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<pre>
-s := make([]int, 10, 100) // slice with len(s) == 10, cap(s) == 100
-s := make([]int, 1e3) // slice with len(s) == cap(s) == 1000
-s := make([]int, 1<<63) // illegal: len(s) is not representable by a value of type int
-s := make([]int, 10, 0) // illegal: len(s) > cap(s)
-c := make(chan int, 10) // channel with a buffer size of 10
-m := make(map[string]int, 100) // map with initial space for approximately 100 elements
-</pre>
-
-<p>
-Calling <code>make</code> with a map type and size hint <code>n</code> will
-create a map with initial space to hold <code>n</code> map elements.
-The precise behavior is implementation-dependent.
-</p>
-
-
-<h3 id="Appending_and_copying_slices">Appending to and copying slices</h3>
-
-<p>
-The built-in functions <code>append</code> and <code>copy</code> assist in
-common slice operations.
-For both functions, the result is independent of whether the memory referenced
-by the arguments overlaps.
-</p>
-
-<p>
-The <a href="#Function_types">variadic</a> function <code>append</code>
-appends zero or more values <code>x</code>
-to <code>s</code> of type <code>S</code>, which must be a slice type, and
-returns the resulting slice, also of type <code>S</code>.
-The values <code>x</code> are passed to a parameter of type <code>...T</code>
-where <code>T</code> is the <a href="#Slice_types">element type</a> of
-<code>S</code> and the respective
-<a href="#Passing_arguments_to_..._parameters">parameter passing rules</a> apply.
-As a special case, <code>append</code> also accepts a first argument
-assignable to type <code>[]byte</code> with a second argument of
-string type followed by <code>...</code>. This form appends the
-bytes of the string.
-</p>
-
-<pre class="grammar">
-append(s S, x ...T) S // T is the element type of S
-</pre>
-
-<p>
-If the capacity of <code>s</code> is not large enough to fit the additional
-values, <code>append</code> allocates a new, sufficiently large underlying
-array that fits both the existing slice elements and the additional values.
-Otherwise, <code>append</code> re-uses the underlying array.
-</p>
-
-<pre>
-s0 := []int{0, 0}
-s1 := append(s0, 2) // append a single element s1 == []int{0, 0, 2}
-s2 := append(s1, 3, 5, 7) // append multiple elements s2 == []int{0, 0, 2, 3, 5, 7}
-s3 := append(s2, s0...) // append a slice s3 == []int{0, 0, 2, 3, 5, 7, 0, 0}
-s4 := append(s3[3:6], s3[2:]...) // append overlapping slice s4 == []int{3, 5, 7, 2, 3, 5, 7, 0, 0}
-
-var t []interface{}
-t = append(t, 42, 3.1415, "foo") // t == []interface{}{42, 3.1415, "foo"}
-
-var b []byte
-b = append(b, "bar"...) // append string contents b == []byte{'b', 'a', 'r' }
-</pre>
-
-<p>
-The function <code>copy</code> copies slice elements from
-a source <code>src</code> to a destination <code>dst</code> and returns the
-number of elements copied.
-Both arguments must have <a href="#Type_identity">identical</a> element type <code>T</code> and must be
-<a href="#Assignability">assignable</a> to a slice of type <code>[]T</code>.
-The number of elements copied is the minimum of
-<code>len(src)</code> and <code>len(dst)</code>.
-As a special case, <code>copy</code> also accepts a destination argument assignable
-to type <code>[]byte</code> with a source argument of a string type.
-This form copies the bytes from the string into the byte slice.
-</p>
-
-<pre class="grammar">
-copy(dst, src []T) int
-copy(dst []byte, src string) int
-</pre>
-
-<p>
-Examples:
-</p>
-
-<pre>
-var a = [...]int{0, 1, 2, 3, 4, 5, 6, 7}
-var s = make([]int, 6)
-var b = make([]byte, 5)
-n1 := copy(s, a[0:]) // n1 == 6, s == []int{0, 1, 2, 3, 4, 5}
-n2 := copy(s, s[2:]) // n2 == 4, s == []int{2, 3, 4, 5, 4, 5}
-n3 := copy(b, "Hello, World!") // n3 == 5, b == []byte("Hello")
-</pre>
-
-
-<h3 id="Deletion_of_map_elements">Deletion of map elements</h3>
-
-<p>
-The built-in function <code>delete</code> removes the element with key
-<code>k</code> from a <a href="#Map_types">map</a> <code>m</code>. The
-type of <code>k</code> must be <a href="#Assignability">assignable</a>
-to the key type of <code>m</code>.
-</p>
-
-<pre class="grammar">
-delete(m, k) // remove element m[k] from map m
-</pre>
-
-<p>
-If the map <code>m</code> is <code>nil</code> or the element <code>m[k]</code>
-does not exist, <code>delete</code> is a no-op.
-</p>
-
-
-<h3 id="Complex_numbers">Manipulating complex numbers</h3>
-
-<p>
-Three functions assemble and disassemble complex numbers.
-The built-in function <code>complex</code> constructs a complex
-value from a floating-point real and imaginary part, while
-<code>real</code> and <code>imag</code>
-extract the real and imaginary parts of a complex value.
-</p>
-
-<pre class="grammar">
-complex(realPart, imaginaryPart floatT) complexT
-real(complexT) floatT
-imag(complexT) floatT
-</pre>
-
-<p>
-The type of the arguments and return value correspond.
-For <code>complex</code>, the two arguments must be of the same
-floating-point type and the return type is the complex type
-with the corresponding floating-point constituents:
-<code>complex64</code> for <code>float32</code> arguments, and
-<code>complex128</code> for <code>float64</code> arguments.
-If one of the arguments evaluates to an untyped constant, it is first implicitly
-<a href="#Conversions">converted</a> to the type of the other argument.
-If both arguments evaluate to untyped constants, they must be non-complex
-numbers or their imaginary parts must be zero, and the return value of
-the function is an untyped complex constant.
-</p>
-
-<p>
-For <code>real</code> and <code>imag</code>, the argument must be
-of complex type, and the return type is the corresponding floating-point
-type: <code>float32</code> for a <code>complex64</code> argument, and
-<code>float64</code> for a <code>complex128</code> argument.
-If the argument evaluates to an untyped constant, it must be a number,
-and the return value of the function is an untyped floating-point constant.
-</p>
-
-<p>
-The <code>real</code> and <code>imag</code> functions together form the inverse of
-<code>complex</code>, so for a value <code>z</code> of a complex type <code>Z</code>,
-<code>z == Z(complex(real(z), imag(z)))</code>.
-</p>
-
-<p>
-If the operands of these functions are all constants, the return
-value is a constant.
-</p>
-
-<pre>
-var a = complex(2, -2) // complex128
-const b = complex(1.0, -1.4) // untyped complex constant 1 - 1.4i
-x := float32(math.Cos(math.Pi/2)) // float32
-var c64 = complex(5, -x) // complex64
-var s int = complex(1, 0) // untyped complex constant 1 + 0i can be converted to int
-_ = complex(1, 2<<s) // illegal: 2 assumes floating-point type, cannot shift
-var rl = real(c64) // float32
-var im = imag(a) // float64
-const c = imag(b) // untyped constant -1.4
-_ = imag(3 << s) // illegal: 3 assumes complex type, cannot shift
-</pre>
-
-<h3 id="Handling_panics">Handling panics</h3>
-
-<p> Two built-in functions, <code>panic</code> and <code>recover</code>,
-assist in reporting and handling <a href="#Run_time_panics">run-time panics</a>
-and program-defined error conditions.
-</p>
-
-<pre class="grammar">
-func panic(interface{})
-func recover() interface{}
-</pre>
-
-<p>
-While executing a function <code>F</code>,
-an explicit call to <code>panic</code> or a <a href="#Run_time_panics">run-time panic</a>
-terminates the execution of <code>F</code>.
-Any functions <a href="#Defer_statements">deferred</a> by <code>F</code>
-are then executed as usual.
-Next, any deferred functions run by <code>F's</code> caller are run,
-and so on up to any deferred by the top-level function in the executing goroutine.
-At that point, the program is terminated and the error
-condition is reported, including the value of the argument to <code>panic</code>.
-This termination sequence is called <i>panicking</i>.
-</p>
-
-<pre>
-panic(42)
-panic("unreachable")
-panic(Error("cannot parse"))
-</pre>
-
-<p>
-The <code>recover</code> function allows a program to manage behavior
-of a panicking goroutine.
-Suppose a function <code>G</code> defers a function <code>D</code> that calls
-<code>recover</code> and a panic occurs in a function on the same goroutine in which <code>G</code>
-is executing.
-When the running of deferred functions reaches <code>D</code>,
-the return value of <code>D</code>'s call to <code>recover</code> will be the value passed to the call of <code>panic</code>.
-If <code>D</code> returns normally, without starting a new
-<code>panic</code>, the panicking sequence stops. In that case,
-the state of functions called between <code>G</code> and the call to <code>panic</code>
-is discarded, and normal execution resumes.
-Any functions deferred by <code>G</code> before <code>D</code> are then run and <code>G</code>'s
-execution terminates by returning to its caller.
-</p>
-
-<p>
-The return value of <code>recover</code> is <code>nil</code> if any of the following conditions holds:
-</p>
-<ul>
-<li>
-<code>panic</code>'s argument was <code>nil</code>;
-</li>
-<li>
-the goroutine is not panicking;
-</li>
-<li>
-<code>recover</code> was not called directly by a deferred function.
-</li>
-</ul>
-
-<p>
-The <code>protect</code> function in the example below invokes
-the function argument <code>g</code> and protects callers from
-run-time panics raised by <code>g</code>.
-</p>
-
-<pre>
-func protect(g func()) {
- defer func() {
- log.Println("done") // Println executes normally even if there is a panic
- if x := recover(); x != nil {
- log.Printf("run time panic: %v", x)
- }
- }()
- log.Println("start")
- g()
-}
-</pre>
-
-
-<h3 id="Bootstrapping">Bootstrapping</h3>
-
-<p>
-Current implementations provide several built-in functions useful during
-bootstrapping. These functions are documented for completeness but are not
-guaranteed to stay in the language. They do not return a result.
-</p>
-
-<pre class="grammar">
-Function Behavior
-
-print prints all arguments; formatting of arguments is implementation-specific
-println like print but prints spaces between arguments and a newline at the end
-</pre>
-
-<p>
-Implementation restriction: <code>print</code> and <code>println</code> need not
-accept arbitrary argument types, but printing of boolean, numeric, and string
-<a href="#Types">types</a> must be supported.
-</p>
-
-<h2 id="Packages">Packages</h2>
-
-<p>
-Go programs are constructed by linking together <i>packages</i>.
-A package in turn is constructed from one or more source files
-that together declare constants, types, variables and functions
-belonging to the package and which are accessible in all files
-of the same package. Those elements may be
-<a href="#Exported_identifiers">exported</a> and used in another package.
-</p>
-
-<h3 id="Source_file_organization">Source file organization</h3>
-
-<p>
-Each source file consists of a package clause defining the package
-to which it belongs, followed by a possibly empty set of import
-declarations that declare packages whose contents it wishes to use,
-followed by a possibly empty set of declarations of functions,
-types, variables, and constants.
-</p>
-
-<pre class="ebnf">
-SourceFile = PackageClause ";" { ImportDecl ";" } { TopLevelDecl ";" } .
-</pre>
-
-<h3 id="Package_clause">Package clause</h3>
-
-<p>
-A package clause begins each source file and defines the package
-to which the file belongs.
-</p>
-
-<pre class="ebnf">
-PackageClause = "package" PackageName .
-PackageName = identifier .
-</pre>
-
-<p>
-The PackageName must not be the <a href="#Blank_identifier">blank identifier</a>.
-</p>
-
-<pre>
-package math
-</pre>
-
-<p>
-A set of files sharing the same PackageName form the implementation of a package.
-An implementation may require that all source files for a package inhabit the same directory.
-</p>
-
-<h3 id="Import_declarations">Import declarations</h3>
-
-<p>
-An import declaration states that the source file containing the declaration
-depends on functionality of the <i>imported</i> package
-(<a href="#Program_initialization_and_execution">§Program initialization and execution</a>)
-and enables access to <a href="#Exported_identifiers">exported</a> identifiers
-of that package.
-The import names an identifier (PackageName) to be used for access and an ImportPath
-that specifies the package to be imported.
-</p>
-
-<pre class="ebnf">
-ImportDecl = "import" ( ImportSpec | "(" { ImportSpec ";" } ")" ) .
-ImportSpec = [ "." | PackageName ] ImportPath .
-ImportPath = string_lit .
-</pre>
-
-<p>
-The PackageName is used in <a href="#Qualified_identifiers">qualified identifiers</a>
-to access exported identifiers of the package within the importing source file.
-It is declared in the <a href="#Blocks">file block</a>.
-If the PackageName is omitted, it defaults to the identifier specified in the
-<a href="#Package_clause">package clause</a> of the imported package.
-If an explicit period (<code>.</code>) appears instead of a name, all the
-package's exported identifiers declared in that package's
-<a href="#Blocks">package block</a> will be declared in the importing source
-file's file block and must be accessed without a qualifier.
-</p>
-
-<p>
-The interpretation of the ImportPath is implementation-dependent but
-it is typically a substring of the full file name of the compiled
-package and may be relative to a repository of installed packages.
-</p>
-
-<p>
-Implementation restriction: A compiler may restrict ImportPaths to
-non-empty strings using only characters belonging to
-<a href="https://www.unicode.org/versions/Unicode6.3.0/">Unicode's</a>
-L, M, N, P, and S general categories (the Graphic characters without
-spaces) and may also exclude the characters
-<code>!"#$%&'()*,:;<=>?[\]^`{|}</code>
-and the Unicode replacement character U+FFFD.
-</p>
-
-<p>
-Assume we have compiled a package containing the package clause
-<code>package math</code>, which exports function <code>Sin</code>, and
-installed the compiled package in the file identified by
-<code>"lib/math"</code>.
-This table illustrates how <code>Sin</code> is accessed in files
-that import the package after the
-various types of import declaration.
-</p>
-
-<pre class="grammar">
-Import declaration Local name of Sin
-
-import "lib/math" math.Sin
-import m "lib/math" m.Sin
-import . "lib/math" Sin
-</pre>
-
-<p>
-An import declaration declares a dependency relation between
-the importing and imported package.
-It is illegal for a package to import itself, directly or indirectly,
-or to directly import a package without
-referring to any of its exported identifiers. To import a package solely for
-its side-effects (initialization), use the <a href="#Blank_identifier">blank</a>
-identifier as explicit package name:
-</p>
-
-<pre>
-import _ "lib/math"
-</pre>
-
-
-<h3 id="An_example_package">An example package</h3>
-
-<p>
-Here is a complete Go package that implements a concurrent prime sieve.
-</p>
-
-<pre>
-package main
-
-import "fmt"
-
-// Send the sequence 2, 3, 4, … to channel 'ch'.
-func generate(ch chan<- int) {
- for i := 2; ; i++ {
- ch <- i // Send 'i' to channel 'ch'.
- }
-}
-
-// Copy the values from channel 'src' to channel 'dst',
-// removing those divisible by 'prime'.
-func filter(src <-chan int, dst chan<- int, prime int) {
- for i := range src { // Loop over values received from 'src'.
- if i%prime != 0 {
- dst <- i // Send 'i' to channel 'dst'.
- }
- }
-}
-
-// The prime sieve: Daisy-chain filter processes together.
-func sieve() {
- ch := make(chan int) // Create a new channel.
- go generate(ch) // Start generate() as a subprocess.
- for {
- prime := <-ch
- fmt.Print(prime, "\n")
- ch1 := make(chan int)
- go filter(ch, ch1, prime)
- ch = ch1
- }
-}
-
-func main() {
- sieve()
-}
-</pre>
-
-<h2 id="Program_initialization_and_execution">Program initialization and execution</h2>
-
-<h3 id="The_zero_value">The zero value</h3>
-<p>
-When storage is allocated for a <a href="#Variables">variable</a>,
-either through a declaration or a call of <code>new</code>, or when
-a new value is created, either through a composite literal or a call
-of <code>make</code>,
-and no explicit initialization is provided, the variable or value is
-given a default value. Each element of such a variable or value is
-set to the <i>zero value</i> for its type: <code>false</code> for booleans,
-<code>0</code> for numeric types, <code>""</code>
-for strings, and <code>nil</code> for pointers, functions, interfaces, slices, channels, and maps.
-This initialization is done recursively, so for instance each element of an
-array of structs will have its fields zeroed if no value is specified.
-</p>
-<p>
-These two simple declarations are equivalent:
-</p>
-
-<pre>
-var i int
-var i int = 0
-</pre>
-
-<p>
-After
-</p>
-
-<pre>
-type T struct { i int; f float64; next *T }
-t := new(T)
-</pre>
-
-<p>
-the following holds:
-</p>
-
-<pre>
-t.i == 0
-t.f == 0.0
-t.next == nil
-</pre>
-
-<p>
-The same would also be true after
-</p>
-
-<pre>
-var t T
-</pre>
-
-<h3 id="Package_initialization">Package initialization</h3>
-
-<p>
-Within a package, package-level variable initialization proceeds stepwise,
-with each step selecting the variable earliest in <i>declaration order</i>
-which has no dependencies on uninitialized variables.
-</p>
-
-<p>
-More precisely, a package-level variable is considered <i>ready for
-initialization</i> if it is not yet initialized and either has
-no <a href="#Variable_declarations">initialization expression</a> or
-its initialization expression has no <i>dependencies</i> on uninitialized variables.
-Initialization proceeds by repeatedly initializing the next package-level
-variable that is earliest in declaration order and ready for initialization,
-until there are no variables ready for initialization.
-</p>
-
-<p>
-If any variables are still uninitialized when this
-process ends, those variables are part of one or more initialization cycles,
-and the program is not valid.
-</p>
-
-<p>
-Multiple variables on the left-hand side of a variable declaration initialized
-by single (multi-valued) expression on the right-hand side are initialized
-together: If any of the variables on the left-hand side is initialized, all
-those variables are initialized in the same step.
-</p>
-
-<pre>
-var x = a
-var a, b = f() // a and b are initialized together, before x is initialized
-</pre>
-
-<p>
-For the purpose of package initialization, <a href="#Blank_identifier">blank</a>
-variables are treated like any other variables in declarations.
-</p>
-
-<p>
-The declaration order of variables declared in multiple files is determined
-by the order in which the files are presented to the compiler: Variables
-declared in the first file are declared before any of the variables declared
-in the second file, and so on.
-</p>
-
-<p>
-Dependency analysis does not rely on the actual values of the
-variables, only on lexical <i>references</i> to them in the source,
-analyzed transitively. For instance, if a variable <code>x</code>'s
-initialization expression refers to a function whose body refers to
-variable <code>y</code> then <code>x</code> depends on <code>y</code>.
-Specifically:
-</p>
-
-<ul>
-<li>
-A reference to a variable or function is an identifier denoting that
-variable or function.
-</li>
-
-<li>
-A reference to a method <code>m</code> is a
-<a href="#Method_values">method value</a> or
-<a href="#Method_expressions">method expression</a> of the form
-<code>t.m</code>, where the (static) type of <code>t</code> is
-not an interface type, and the method <code>m</code> is in the
-<a href="#Method_sets">method set</a> of <code>t</code>.
-It is immaterial whether the resulting function value
-<code>t.m</code> is invoked.
-</li>
-
-<li>
-A variable, function, or method <code>x</code> depends on a variable
-<code>y</code> if <code>x</code>'s initialization expression or body
-(for functions and methods) contains a reference to <code>y</code>
-or to a function or method that depends on <code>y</code>.
-</li>
-</ul>
-
-<p>
-For example, given the declarations
-</p>
-
-<pre>
-var (
- a = c + b // == 9
- b = f() // == 4
- c = f() // == 5
- d = 3 // == 5 after initialization has finished
-)
-
-func f() int {
- d++
- return d
-}
-</pre>
-
-<p>
-the initialization order is <code>d</code>, <code>b</code>, <code>c</code>, <code>a</code>.
-Note that the order of subexpressions in initialization expressions is irrelevant:
-<code>a = c + b</code> and <code>a = b + c</code> result in the same initialization
-order in this example.
-</p>
-
-<p>
-Dependency analysis is performed per package; only references referring
-to variables, functions, and (non-interface) methods declared in the current
-package are considered. If other, hidden, data dependencies exists between
-variables, the initialization order between those variables is unspecified.
-</p>
-
-<p>
-For instance, given the declarations
-</p>
-
-<pre>
-var x = I(T{}).ab() // x has an undetected, hidden dependency on a and b
-var _ = sideEffect() // unrelated to x, a, or b
-var a = b
-var b = 42
-
-type I interface { ab() []int }
-type T struct{}
-func (T) ab() []int { return []int{a, b} }
-</pre>
-
-<p>
-the variable <code>a</code> will be initialized after <code>b</code> but
-whether <code>x</code> is initialized before <code>b</code>, between
-<code>b</code> and <code>a</code>, or after <code>a</code>, and
-thus also the moment at which <code>sideEffect()</code> is called (before
-or after <code>x</code> is initialized) is not specified.
-</p>
-
-<p>
-Variables may also be initialized using functions named <code>init</code>
-declared in the package block, with no arguments and no result parameters.
-</p>
-
-<pre>
-func init() { … }
-</pre>
-
-<p>
-Multiple such functions may be defined per package, even within a single
-source file. In the package block, the <code>init</code> identifier can
-be used only to declare <code>init</code> functions, yet the identifier
-itself is not <a href="#Declarations_and_scope">declared</a>. Thus
-<code>init</code> functions cannot be referred to from anywhere
-in a program.
-</p>
-
-<p>
-A package with no imports is initialized by assigning initial values
-to all its package-level variables followed by calling all <code>init</code>
-functions in the order they appear in the source, possibly in multiple files,
-as presented to the compiler.
-If a package has imports, the imported packages are initialized
-before initializing the package itself. If multiple packages import
-a package, the imported package will be initialized only once.
-The importing of packages, by construction, guarantees that there
-can be no cyclic initialization dependencies.
-</p>
-
-<p>
-Package initialization—variable initialization and the invocation of
-<code>init</code> functions—happens in a single goroutine,
-sequentially, one package at a time.
-An <code>init</code> function may launch other goroutines, which can run
-concurrently with the initialization code. However, initialization
-always sequences
-the <code>init</code> functions: it will not invoke the next one
-until the previous one has returned.
-</p>
-
-<p>
-To ensure reproducible initialization behavior, build systems are encouraged
-to present multiple files belonging to the same package in lexical file name
-order to a compiler.
-</p>
-
-
-<h3 id="Program_execution">Program execution</h3>
-<p>
-A complete program is created by linking a single, unimported package
-called the <i>main package</i> with all the packages it imports, transitively.
-The main package must
-have package name <code>main</code> and
-declare a function <code>main</code> that takes no
-arguments and returns no value.
-</p>
-
-<pre>
-func main() { … }
-</pre>
-
-<p>
-Program execution begins by initializing the main package and then
-invoking the function <code>main</code>.
-When that function invocation returns, the program exits.
-It does not wait for other (non-<code>main</code>) goroutines to complete.
-</p>
-
-<h2 id="Errors">Errors</h2>
-
-<p>
-The predeclared type <code>error</code> is defined as
-</p>
-
-<pre>
-type error interface {
- Error() string
-}
-</pre>
-
-<p>
-It is the conventional interface for representing an error condition,
-with the nil value representing no error.
-For instance, a function to read data from a file might be defined:
-</p>
-
-<pre>
-func Read(f *File, b []byte) (n int, err error)
-</pre>
-
-<h2 id="Run_time_panics">Run-time panics</h2>
-
-<p>
-Execution errors such as attempting to index an array out
-of bounds trigger a <i>run-time panic</i> equivalent to a call of
-the built-in function <a href="#Handling_panics"><code>panic</code></a>
-with a value of the implementation-defined interface type <code>runtime.Error</code>.
-That type satisfies the predeclared interface type
-<a href="#Errors"><code>error</code></a>.
-The exact error values that
-represent distinct run-time error conditions are unspecified.
-</p>
-
-<pre>
-package runtime
-
-type Error interface {
- error
- // and perhaps other methods
-}
-</pre>
-
-<h2 id="System_considerations">System considerations</h2>
-
-<h3 id="Package_unsafe">Package <code>unsafe</code></h3>
-
-<p>
-The built-in package <code>unsafe</code>, known to the compiler
-and accessible through the <a href="#Import_declarations">import path</a> <code>"unsafe"</code>,
-provides facilities for low-level programming including operations
-that violate the type system. A package using <code>unsafe</code>
-must be vetted manually for type safety and may not be portable.
-The package provides the following interface:
-</p>
-
-<pre class="grammar">
-package unsafe
-
-type ArbitraryType int // shorthand for an arbitrary Go type; it is not a real type
-type Pointer *ArbitraryType
-
-func Alignof(variable ArbitraryType) uintptr
-func Offsetof(selector ArbitraryType) uintptr
-func Sizeof(variable ArbitraryType) uintptr
-
-type IntegerType int // shorthand for an integer type; it is not a real type
-func Add(ptr Pointer, len IntegerType) Pointer
-func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType
-</pre>
-
-<p>
-A <code>Pointer</code> is a <a href="#Pointer_types">pointer type</a> but a <code>Pointer</code>
-value may not be <a href="#Address_operators">dereferenced</a>.
-Any pointer or value of <a href="#Types">underlying type</a> <code>uintptr</code> can be converted to
-a type of underlying type <code>Pointer</code> and vice versa.
-The effect of converting between <code>Pointer</code> and <code>uintptr</code> is implementation-defined.
-</p>
-
-<pre>
-var f float64
-bits = *(*uint64)(unsafe.Pointer(&f))
-
-type ptr unsafe.Pointer
-bits = *(*uint64)(ptr(&f))
-
-var p ptr = nil
-</pre>
-
-<p>
-The functions <code>Alignof</code> and <code>Sizeof</code> take an expression <code>x</code>
-of any type and return the alignment or size, respectively, of a hypothetical variable <code>v</code>
-as if <code>v</code> was declared via <code>var v = x</code>.
-</p>
-<p>
-The function <code>Offsetof</code> takes a (possibly parenthesized) <a href="#Selectors">selector</a>
-<code>s.f</code>, denoting a field <code>f</code> of the struct denoted by <code>s</code>
-or <code>*s</code>, and returns the field offset in bytes relative to the struct's address.
-If <code>f</code> is an <a href="#Struct_types">embedded field</a>, it must be reachable
-without pointer indirections through fields of the struct.
-For a struct <code>s</code> with field <code>f</code>:
-</p>
-
-<pre>
-uintptr(unsafe.Pointer(&s)) + unsafe.Offsetof(s.f) == uintptr(unsafe.Pointer(&s.f))
-</pre>
-
-<p>
-Computer architectures may require memory addresses to be <i>aligned</i>;
-that is, for addresses of a variable to be a multiple of a factor,
-the variable's type's <i>alignment</i>. The function <code>Alignof</code>
-takes an expression denoting a variable of any type and returns the
-alignment of the (type of the) variable in bytes. For a variable
-<code>x</code>:
-</p>
-
-<pre>
-uintptr(unsafe.Pointer(&x)) % unsafe.Alignof(x) == 0
-</pre>
-
-<p>
-Calls to <code>Alignof</code>, <code>Offsetof</code>, and
-<code>Sizeof</code> are compile-time constant expressions of type <code>uintptr</code>.
-</p>
-
-<p>
-The function <code>Add</code> adds <code>len</code> to <code>ptr</code>
-and returns the updated pointer <code>unsafe.Pointer(uintptr(ptr) + uintptr(len))</code>.
-The <code>len</code> argument must be of integer type or an untyped <a href="#Constants">constant</a>.
-A constant <code>len</code> argument must be <a href="#Representability">representable</a> by a value of type <code>int</code>;
-if it is an untyped constant it is given type <code>int</code>.
-The rules for <a href="/pkg/unsafe#Pointer">valid uses</a> of <code>Pointer</code> still apply.
-</p>
-
-<p>
-The function <code>Slice</code> returns a slice whose underlying array starts at <code>ptr</code>
-and whose length and capacity are <code>len</code>.
-<code>Slice(ptr, len)</code> is equivalent to
-</p>
-
-<pre>
-(*[len]ArbitraryType)(unsafe.Pointer(ptr))[:]
-</pre>
-
-<p>
-except that, as a special case, if <code>ptr</code>
-is <code>nil</code> and <code>len</code> is zero,
-<code>Slice</code> returns <code>nil</code>.
-</p>
-
-<p>
-The <code>len</code> argument must be of integer type or an untyped <a href="#Constants">constant</a>.
-A constant <code>len</code> argument must be non-negative and <a href="#Representability">representable</a> by a value of type <code>int</code>;
-if it is an untyped constant it is given type <code>int</code>.
-At run time, if <code>len</code> is negative,
-or if <code>ptr</code> is <code>nil</code> and <code>len</code> is not zero,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<h3 id="Size_and_alignment_guarantees">Size and alignment guarantees</h3>
-
-<p>
-For the <a href="#Numeric_types">numeric types</a>, the following sizes are guaranteed:
-</p>
-
-<pre class="grammar">
-type size in bytes
-
-byte, uint8, int8 1
-uint16, int16 2
-uint32, int32, float32 4
-uint64, int64, float64, complex64 8
-complex128 16
-</pre>
-
-<p>
-The following minimal alignment properties are guaranteed:
-</p>
-<ol>
-<li>For a variable <code>x</code> of any type: <code>unsafe.Alignof(x)</code> is at least 1.
-</li>
-
-<li>For a variable <code>x</code> of struct type: <code>unsafe.Alignof(x)</code> is the largest of
- all the values <code>unsafe.Alignof(x.f)</code> for each field <code>f</code> of <code>x</code>, but at least 1.
-</li>
-
-<li>For a variable <code>x</code> of array type: <code>unsafe.Alignof(x)</code> is the same as
- the alignment of a variable of the array's element type.
-</li>
-</ol>
-
-<p>
-A struct or array type has size zero if it contains no fields (or elements, respectively) that have a size greater than zero. Two distinct zero-size variables may have the same address in memory.
-</p>
diff --git a/_content/ref/spec.html b/_content/ref/spec.html
deleted file mode 100644
index 197acc5..0000000
--- a/_content/ref/spec.html
+++ /dev/null
@@ -1,8060 +0,0 @@
-<!--{
- "Title": "The Go Programming Language Specification",
- "Subtitle": "Version of March 10, 2022"
-}-->
-
-<h2 id="Introduction">Introduction</h2>
-
-<p>
-This is the reference manual for the Go programming language.
-The pre-Go1.18 version, without generics, can be found
-<a href="/doc/go1.17_spec.html">here</a>.
-For more information and other documents, see <a href="/">golang.org</a>.
-</p>
-
-<p>
-Go is a general-purpose language designed with systems programming
-in mind. It is strongly typed and garbage-collected and has explicit
-support for concurrent programming. Programs are constructed from
-<i>packages</i>, whose properties allow efficient management of
-dependencies.
-</p>
-
-<p>
-The grammar is compact and simple to parse, allowing for easy analysis
-by automatic tools such as integrated development environments.
-</p>
-
-<h2 id="Notation">Notation</h2>
-<p>
-The syntax is specified using Extended Backus-Naur Form (EBNF):
-</p>
-
-<pre class="grammar">
-Production = production_name "=" [ Expression ] "." .
-Expression = Alternative { "|" Alternative } .
-Alternative = Term { Term } .
-Term = production_name | token [ "…" token ] | Group | Option | Repetition .
-Group = "(" Expression ")" .
-Option = "[" Expression "]" .
-Repetition = "{" Expression "}" .
-</pre>
-
-<p>
-Productions are expressions constructed from terms and the following
-operators, in increasing precedence:
-</p>
-<pre class="grammar">
-| alternation
-() grouping
-[] option (0 or 1 times)
-{} repetition (0 to n times)
-</pre>
-
-<p>
-Lower-case production names are used to identify lexical tokens.
-Non-terminals are in CamelCase. Lexical tokens are enclosed in
-double quotes <code>""</code> or back quotes <code>``</code>.
-</p>
-
-<p>
-The form <code>a … b</code> represents the set of characters from
-<code>a</code> through <code>b</code> as alternatives. The horizontal
-ellipsis <code>…</code> is also used elsewhere in the spec to informally denote various
-enumerations or code snippets that are not further specified. The character <code>…</code>
-(as opposed to the three characters <code>...</code>) is not a token of the Go
-language.
-</p>
-
-<h2 id="Source_code_representation">Source code representation</h2>
-
-<p>
-Source code is Unicode text encoded in
-<a href="https://en.wikipedia.org/wiki/UTF-8">UTF-8</a>. The text is not
-canonicalized, so a single accented code point is distinct from the
-same character constructed from combining an accent and a letter;
-those are treated as two code points. For simplicity, this document
-will use the unqualified term <i>character</i> to refer to a Unicode code point
-in the source text.
-</p>
-<p>
-Each code point is distinct; for instance, upper and lower case letters
-are different characters.
-</p>
-<p>
-Implementation restriction: For compatibility with other tools, a
-compiler may disallow the NUL character (U+0000) in the source text.
-</p>
-<p>
-Implementation restriction: For compatibility with other tools, a
-compiler may ignore a UTF-8-encoded byte order mark
-(U+FEFF) if it is the first Unicode code point in the source text.
-A byte order mark may be disallowed anywhere else in the source.
-</p>
-
-<h3 id="Characters">Characters</h3>
-
-<p>
-The following terms are used to denote specific Unicode character classes:
-</p>
-<pre class="ebnf">
-newline = /* the Unicode code point U+000A */ .
-unicode_char = /* an arbitrary Unicode code point except newline */ .
-unicode_letter = /* a Unicode code point classified as "Letter" */ .
-unicode_digit = /* a Unicode code point classified as "Number, decimal digit" */ .
-</pre>
-
-<p>
-In <a href="https://www.unicode.org/versions/Unicode8.0.0/">The Unicode Standard 8.0</a>,
-Section 4.5 "General Category" defines a set of character categories.
-Go treats all characters in any of the Letter categories Lu, Ll, Lt, Lm, or Lo
-as Unicode letters, and those in the Number category Nd as Unicode digits.
-</p>
-
-<h3 id="Letters_and_digits">Letters and digits</h3>
-
-<p>
-The underscore character <code>_</code> (U+005F) is considered a letter.
-</p>
-<pre class="ebnf">
-letter = unicode_letter | "_" .
-decimal_digit = "0" … "9" .
-binary_digit = "0" | "1" .
-octal_digit = "0" … "7" .
-hex_digit = "0" … "9" | "A" … "F" | "a" … "f" .
-</pre>
-
-<h2 id="Lexical_elements">Lexical elements</h2>
-
-<h3 id="Comments">Comments</h3>
-
-<p>
-Comments serve as program documentation. There are two forms:
-</p>
-
-<ol>
-<li>
-<i>Line comments</i> start with the character sequence <code>//</code>
-and stop at the end of the line.
-</li>
-<li>
-<i>General comments</i> start with the character sequence <code>/*</code>
-and stop with the first subsequent character sequence <code>*/</code>.
-</li>
-</ol>
-
-<p>
-A comment cannot start inside a <a href="#Rune_literals">rune</a> or
-<a href="#String_literals">string literal</a>, or inside a comment.
-A general comment containing no newlines acts like a space.
-Any other comment acts like a newline.
-</p>
-
-<h3 id="Tokens">Tokens</h3>
-
-<p>
-Tokens form the vocabulary of the Go language.
-There are four classes: <i>identifiers</i>, <i>keywords</i>, <i>operators
-and punctuation</i>, and <i>literals</i>. <i>White space</i>, formed from
-spaces (U+0020), horizontal tabs (U+0009),
-carriage returns (U+000D), and newlines (U+000A),
-is ignored except as it separates tokens
-that would otherwise combine into a single token. Also, a newline or end of file
-may trigger the insertion of a <a href="#Semicolons">semicolon</a>.
-While breaking the input into tokens,
-the next token is the longest sequence of characters that form a
-valid token.
-</p>
-
-<h3 id="Semicolons">Semicolons</h3>
-
-<p>
-The formal grammar uses semicolons <code>";"</code> as terminators in
-a number of productions. Go programs may omit most of these semicolons
-using the following two rules:
-</p>
-
-<ol>
-<li>
-When the input is broken into tokens, a semicolon is automatically inserted
-into the token stream immediately after a line's final token if that token is
-<ul>
- <li>an
- <a href="#Identifiers">identifier</a>
- </li>
-
- <li>an
- <a href="#Integer_literals">integer</a>,
- <a href="#Floating-point_literals">floating-point</a>,
- <a href="#Imaginary_literals">imaginary</a>,
- <a href="#Rune_literals">rune</a>, or
- <a href="#String_literals">string</a> literal
- </li>
-
- <li>one of the <a href="#Keywords">keywords</a>
- <code>break</code>,
- <code>continue</code>,
- <code>fallthrough</code>, or
- <code>return</code>
- </li>
-
- <li>one of the <a href="#Operators_and_punctuation">operators and punctuation</a>
- <code>++</code>,
- <code>--</code>,
- <code>)</code>,
- <code>]</code>, or
- <code>}</code>
- </li>
-</ul>
-</li>
-
-<li>
-To allow complex statements to occupy a single line, a semicolon
-may be omitted before a closing <code>")"</code> or <code>"}"</code>.
-</li>
-</ol>
-
-<p>
-To reflect idiomatic use, code examples in this document elide semicolons
-using these rules.
-</p>
-
-
-<h3 id="Identifiers">Identifiers</h3>
-
-<p>
-Identifiers name program entities such as variables and types.
-An identifier is a sequence of one or more letters and digits.
-The first character in an identifier must be a letter.
-</p>
-<pre class="ebnf">
-identifier = letter { letter | unicode_digit } .
-</pre>
-<pre>
-a
-_x9
-ThisVariableIsExported
-αβ
-</pre>
-
-<p>
-Some identifiers are <a href="#Predeclared_identifiers">predeclared</a>.
-</p>
-
-
-<h3 id="Keywords">Keywords</h3>
-
-<p>
-The following keywords are reserved and may not be used as identifiers.
-</p>
-<pre class="grammar">
-break default func interface select
-case defer go map struct
-chan else goto package switch
-const fallthrough if range type
-continue for import return var
-</pre>
-
-<h3 id="Operators_and_punctuation">Operators and punctuation</h3>
-
-<p>
-The following character sequences represent <a href="#Operators">operators</a>
-(including <a href="#Assignments">assignment operators</a>) and punctuation:
-</p>
-<pre class="grammar">
-+ & += &= && == != ( )
-- | -= |= || < <= [ ]
-* ^ *= ^= <- > >= { }
-/ << /= <<= ++ = := , ;
-% >> %= >>= -- ! ... . :
- &^ &^= ~
-</pre>
-
-<h3 id="Integer_literals">Integer literals</h3>
-
-<p>
-An integer literal is a sequence of digits representing an
-<a href="#Constants">integer constant</a>.
-An optional prefix sets a non-decimal base: <code>0b</code> or <code>0B</code>
-for binary, <code>0</code>, <code>0o</code>, or <code>0O</code> for octal,
-and <code>0x</code> or <code>0X</code> for hexadecimal.
-A single <code>0</code> is considered a decimal zero.
-In hexadecimal literals, letters <code>a</code> through <code>f</code>
-and <code>A</code> through <code>F</code> represent values 10 through 15.
-</p>
-
-<p>
-For readability, an underscore character <code>_</code> may appear after
-a base prefix or between successive digits; such underscores do not change
-the literal's value.
-</p>
-<pre class="ebnf">
-int_lit = decimal_lit | binary_lit | octal_lit | hex_lit .
-decimal_lit = "0" | ( "1" … "9" ) [ [ "_" ] decimal_digits ] .
-binary_lit = "0" ( "b" | "B" ) [ "_" ] binary_digits .
-octal_lit = "0" [ "o" | "O" ] [ "_" ] octal_digits .
-hex_lit = "0" ( "x" | "X" ) [ "_" ] hex_digits .
-
-decimal_digits = decimal_digit { [ "_" ] decimal_digit } .
-binary_digits = binary_digit { [ "_" ] binary_digit } .
-octal_digits = octal_digit { [ "_" ] octal_digit } .
-hex_digits = hex_digit { [ "_" ] hex_digit } .
-</pre>
-
-<pre>
-42
-4_2
-0600
-0_600
-0o600
-0O600 // second character is capital letter 'O'
-0xBadFace
-0xBad_Face
-0x_67_7a_2f_cc_40_c6
-170141183460469231731687303715884105727
-170_141183_460469_231731_687303_715884_105727
-
-_42 // an identifier, not an integer literal
-42_ // invalid: _ must separate successive digits
-4__2 // invalid: only one _ at a time
-0_xBadFace // invalid: _ must separate successive digits
-</pre>
-
-
-<h3 id="Floating-point_literals">Floating-point literals</h3>
-
-<p>
-A floating-point literal is a decimal or hexadecimal representation of a
-<a href="#Constants">floating-point constant</a>.
-</p>
-
-<p>
-A decimal floating-point literal consists of an integer part (decimal digits),
-a decimal point, a fractional part (decimal digits), and an exponent part
-(<code>e</code> or <code>E</code> followed by an optional sign and decimal digits).
-One of the integer part or the fractional part may be elided; one of the decimal point
-or the exponent part may be elided.
-An exponent value exp scales the mantissa (integer and fractional part) by 10<sup>exp</sup>.
-</p>
-
-<p>
-A hexadecimal floating-point literal consists of a <code>0x</code> or <code>0X</code>
-prefix, an integer part (hexadecimal digits), a radix point, a fractional part (hexadecimal digits),
-and an exponent part (<code>p</code> or <code>P</code> followed by an optional sign and decimal digits).
-One of the integer part or the fractional part may be elided; the radix point may be elided as well,
-but the exponent part is required. (This syntax matches the one given in IEEE 754-2008 §5.12.3.)
-An exponent value exp scales the mantissa (integer and fractional part) by 2<sup>exp</sup>.
-</p>
-
-<p>
-For readability, an underscore character <code>_</code> may appear after
-a base prefix or between successive digits; such underscores do not change
-the literal value.
-</p>
-
-<pre class="ebnf">
-float_lit = decimal_float_lit | hex_float_lit .
-
-decimal_float_lit = decimal_digits "." [ decimal_digits ] [ decimal_exponent ] |
- decimal_digits decimal_exponent |
- "." decimal_digits [ decimal_exponent ] .
-decimal_exponent = ( "e" | "E" ) [ "+" | "-" ] decimal_digits .
-
-hex_float_lit = "0" ( "x" | "X" ) hex_mantissa hex_exponent .
-hex_mantissa = [ "_" ] hex_digits "." [ hex_digits ] |
- [ "_" ] hex_digits |
- "." hex_digits .
-hex_exponent = ( "p" | "P" ) [ "+" | "-" ] decimal_digits .
-</pre>
-
-<pre>
-0.
-72.40
-072.40 // == 72.40
-2.71828
-1.e+0
-6.67428e-11
-1E6
-.25
-.12345E+5
-1_5. // == 15.0
-0.15e+0_2 // == 15.0
-
-0x1p-2 // == 0.25
-0x2.p10 // == 2048.0
-0x1.Fp+0 // == 1.9375
-0X.8p-0 // == 0.5
-0X_1FFFP-16 // == 0.1249847412109375
-0x15e-2 // == 0x15e - 2 (integer subtraction)
-
-0x.p1 // invalid: mantissa has no digits
-1p-2 // invalid: p exponent requires hexadecimal mantissa
-0x1.5e-2 // invalid: hexadecimal mantissa requires p exponent
-1_.5 // invalid: _ must separate successive digits
-1._5 // invalid: _ must separate successive digits
-1.5_e1 // invalid: _ must separate successive digits
-1.5e_1 // invalid: _ must separate successive digits
-1.5e1_ // invalid: _ must separate successive digits
-</pre>
-
-
-<h3 id="Imaginary_literals">Imaginary literals</h3>
-
-<p>
-An imaginary literal represents the imaginary part of a
-<a href="#Constants">complex constant</a>.
-It consists of an <a href="#Integer_literals">integer</a> or
-<a href="#Floating-point_literals">floating-point</a> literal
-followed by the lower-case letter <code>i</code>.
-The value of an imaginary literal is the value of the respective
-integer or floating-point literal multiplied by the imaginary unit <i>i</i>.
-</p>
-
-<pre class="ebnf">
-imaginary_lit = (decimal_digits | int_lit | float_lit) "i" .
-</pre>
-
-<p>
-For backward compatibility, an imaginary literal's integer part consisting
-entirely of decimal digits (and possibly underscores) is considered a decimal
-integer, even if it starts with a leading <code>0</code>.
-</p>
-
-<pre>
-0i
-0123i // == 123i for backward-compatibility
-0o123i // == 0o123 * 1i == 83i
-0xabci // == 0xabc * 1i == 2748i
-0.i
-2.71828i
-1.e+0i
-6.67428e-11i
-1E6i
-.25i
-.12345E+5i
-0x1p-2i // == 0x1p-2 * 1i == 0.25i
-</pre>
-
-
-<h3 id="Rune_literals">Rune literals</h3>
-
-<p>
-A rune literal represents a <a href="#Constants">rune constant</a>,
-an integer value identifying a Unicode code point.
-A rune literal is expressed as one or more characters enclosed in single quotes,
-as in <code>'x'</code> or <code>'\n'</code>.
-Within the quotes, any character may appear except newline and unescaped single
-quote. A single quoted character represents the Unicode value
-of the character itself,
-while multi-character sequences beginning with a backslash encode
-values in various formats.
-</p>
-
-<p>
-The simplest form represents the single character within the quotes;
-since Go source text is Unicode characters encoded in UTF-8, multiple
-UTF-8-encoded bytes may represent a single integer value. For
-instance, the literal <code>'a'</code> holds a single byte representing
-a literal <code>a</code>, Unicode U+0061, value <code>0x61</code>, while
-<code>'ä'</code> holds two bytes (<code>0xc3</code> <code>0xa4</code>) representing
-a literal <code>a</code>-dieresis, U+00E4, value <code>0xe4</code>.
-</p>
-
-<p>
-Several backslash escapes allow arbitrary values to be encoded as
-ASCII text. There are four ways to represent the integer value
-as a numeric constant: <code>\x</code> followed by exactly two hexadecimal
-digits; <code>\u</code> followed by exactly four hexadecimal digits;
-<code>\U</code> followed by exactly eight hexadecimal digits, and a
-plain backslash <code>\</code> followed by exactly three octal digits.
-In each case the value of the literal is the value represented by
-the digits in the corresponding base.
-</p>
-
-<p>
-Although these representations all result in an integer, they have
-different valid ranges. Octal escapes must represent a value between
-0 and 255 inclusive. Hexadecimal escapes satisfy this condition
-by construction. The escapes <code>\u</code> and <code>\U</code>
-represent Unicode code points so within them some values are illegal,
-in particular those above <code>0x10FFFF</code> and surrogate halves.
-</p>
-
-<p>
-After a backslash, certain single-character escapes represent special values:
-</p>
-
-<pre class="grammar">
-\a U+0007 alert or bell
-\b U+0008 backspace
-\f U+000C form feed
-\n U+000A line feed or newline
-\r U+000D carriage return
-\t U+0009 horizontal tab
-\v U+000B vertical tab
-\\ U+005C backslash
-\' U+0027 single quote (valid escape only within rune literals)
-\" U+0022 double quote (valid escape only within string literals)
-</pre>
-
-<p>
-All other sequences starting with a backslash are illegal inside rune literals.
-</p>
-<pre class="ebnf">
-rune_lit = "'" ( unicode_value | byte_value ) "'" .
-unicode_value = unicode_char | little_u_value | big_u_value | escaped_char .
-byte_value = octal_byte_value | hex_byte_value .
-octal_byte_value = `\` octal_digit octal_digit octal_digit .
-hex_byte_value = `\` "x" hex_digit hex_digit .
-little_u_value = `\` "u" hex_digit hex_digit hex_digit hex_digit .
-big_u_value = `\` "U" hex_digit hex_digit hex_digit hex_digit
- hex_digit hex_digit hex_digit hex_digit .
-escaped_char = `\` ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | `\` | "'" | `"` ) .
-</pre>
-
-<pre>
-'a'
-'ä'
-'本'
-'\t'
-'\000'
-'\007'
-'\377'
-'\x07'
-'\xff'
-'\u12e4'
-'\U00101234'
-'\'' // rune literal containing single quote character
-'aa' // illegal: too many characters
-'\xa' // illegal: too few hexadecimal digits
-'\0' // illegal: too few octal digits
-'\uDFFF' // illegal: surrogate half
-'\U00110000' // illegal: invalid Unicode code point
-</pre>
-
-
-<h3 id="String_literals">String literals</h3>
-
-<p>
-A string literal represents a <a href="#Constants">string constant</a>
-obtained from concatenating a sequence of characters. There are two forms:
-raw string literals and interpreted string literals.
-</p>
-
-<p>
-Raw string literals are character sequences between back quotes, as in
-<code>`foo`</code>. Within the quotes, any character may appear except
-back quote. The value of a raw string literal is the
-string composed of the uninterpreted (implicitly UTF-8-encoded) characters
-between the quotes;
-in particular, backslashes have no special meaning and the string may
-contain newlines.
-Carriage return characters ('\r') inside raw string literals
-are discarded from the raw string value.
-</p>
-
-<p>
-Interpreted string literals are character sequences between double
-quotes, as in <code>"bar"</code>.
-Within the quotes, any character may appear except newline and unescaped double quote.
-The text between the quotes forms the
-value of the literal, with backslash escapes interpreted as they
-are in <a href="#Rune_literals">rune literals</a> (except that <code>\'</code> is illegal and
-<code>\"</code> is legal), with the same restrictions.
-The three-digit octal (<code>\</code><i>nnn</i>)
-and two-digit hexadecimal (<code>\x</code><i>nn</i>) escapes represent individual
-<i>bytes</i> of the resulting string; all other escapes represent
-the (possibly multi-byte) UTF-8 encoding of individual <i>characters</i>.
-Thus inside a string literal <code>\377</code> and <code>\xFF</code> represent
-a single byte of value <code>0xFF</code>=255, while <code>ÿ</code>,
-<code>\u00FF</code>, <code>\U000000FF</code> and <code>\xc3\xbf</code> represent
-the two bytes <code>0xc3</code> <code>0xbf</code> of the UTF-8 encoding of character
-U+00FF.
-</p>
-
-<pre class="ebnf">
-string_lit = raw_string_lit | interpreted_string_lit .
-raw_string_lit = "`" { unicode_char | newline } "`" .
-interpreted_string_lit = `"` { unicode_value | byte_value } `"` .
-</pre>
-
-<pre>
-`abc` // same as "abc"
-`\n
-\n` // same as "\\n\n\\n"
-"\n"
-"\"" // same as `"`
-"Hello, world!\n"
-"日本語"
-"\u65e5本\U00008a9e"
-"\xff\u00FF"
-"\uD800" // illegal: surrogate half
-"\U00110000" // illegal: invalid Unicode code point
-</pre>
-
-<p>
-These examples all represent the same string:
-</p>
-
-<pre>
-"日本語" // UTF-8 input text
-`日本語` // UTF-8 input text as a raw literal
-"\u65e5\u672c\u8a9e" // the explicit Unicode code points
-"\U000065e5\U0000672c\U00008a9e" // the explicit Unicode code points
-"\xe6\x97\xa5\xe6\x9c\xac\xe8\xaa\x9e" // the explicit UTF-8 bytes
-</pre>
-
-<p>
-If the source code represents a character as two code points, such as
-a combining form involving an accent and a letter, the result will be
-an error if placed in a rune literal (it is not a single code
-point), and will appear as two code points if placed in a string
-literal.
-</p>
-
-
-<h2 id="Constants">Constants</h2>
-
-<p>There are <i>boolean constants</i>,
-<i>rune constants</i>,
-<i>integer constants</i>,
-<i>floating-point constants</i>, <i>complex constants</i>,
-and <i>string constants</i>. Rune, integer, floating-point,
-and complex constants are
-collectively called <i>numeric constants</i>.
-</p>
-
-<p>
-A constant value is represented by a
-<a href="#Rune_literals">rune</a>,
-<a href="#Integer_literals">integer</a>,
-<a href="#Floating-point_literals">floating-point</a>,
-<a href="#Imaginary_literals">imaginary</a>,
-or
-<a href="#String_literals">string</a> literal,
-an identifier denoting a constant,
-a <a href="#Constant_expressions">constant expression</a>,
-a <a href="#Conversions">conversion</a> with a result that is a constant, or
-the result value of some built-in functions such as
-<code>unsafe.Sizeof</code> applied to <a href="#Package_unsafe">certain values</a>,
-<code>cap</code> or <code>len</code> applied to
-<a href="#Length_and_capacity">some expressions</a>,
-<code>real</code> and <code>imag</code> applied to a complex constant
-and <code>complex</code> applied to numeric constants.
-The boolean truth values are represented by the predeclared constants
-<code>true</code> and <code>false</code>. The predeclared identifier
-<a href="#Iota">iota</a> denotes an integer constant.
-</p>
-
-<p>
-In general, complex constants are a form of
-<a href="#Constant_expressions">constant expression</a>
-and are discussed in that section.
-</p>
-
-<p>
-Numeric constants represent exact values of arbitrary precision and do not overflow.
-Consequently, there are no constants denoting the IEEE-754 negative zero, infinity,
-and not-a-number values.
-</p>
-
-<p>
-Constants may be <a href="#Types">typed</a> or <i>untyped</i>.
-Literal constants, <code>true</code>, <code>false</code>, <code>iota</code>,
-and certain <a href="#Constant_expressions">constant expressions</a>
-containing only untyped constant operands are untyped.
-</p>
-
-<p>
-A constant may be given a type explicitly by a <a href="#Constant_declarations">constant declaration</a>
-or <a href="#Conversions">conversion</a>, or implicitly when used in a
-<a href="#Variable_declarations">variable declaration</a> or an
-<a href="#Assignments">assignment</a> or as an
-operand in an <a href="#Expressions">expression</a>.
-It is an error if the constant value
-cannot be <a href="#Representability">represented</a> as a value of the respective type.
-If the type is a type parameter, the constant is converted into a non-constant
-value of the type parameter.
-</p>
-
-<p>
-An untyped constant has a <i>default type</i> which is the type to which the
-constant is implicitly converted in contexts where a typed value is required,
-for instance, in a <a href="#Short_variable_declarations">short variable declaration</a>
-such as <code>i := 0</code> where there is no explicit type.
-The default type of an untyped constant is <code>bool</code>, <code>rune</code>,
-<code>int</code>, <code>float64</code>, <code>complex128</code> or <code>string</code>
-respectively, depending on whether it is a boolean, rune, integer, floating-point,
-complex, or string constant.
-</p>
-
-<p>
-Implementation restriction: Although numeric constants have arbitrary
-precision in the language, a compiler may implement them using an
-internal representation with limited precision. That said, every
-implementation must:
-</p>
-
-<ul>
- <li>Represent integer constants with at least 256 bits.</li>
-
- <li>Represent floating-point constants, including the parts of
- a complex constant, with a mantissa of at least 256 bits
- and a signed binary exponent of at least 16 bits.</li>
-
- <li>Give an error if unable to represent an integer constant
- precisely.</li>
-
- <li>Give an error if unable to represent a floating-point or
- complex constant due to overflow.</li>
-
- <li>Round to the nearest representable constant if unable to
- represent a floating-point or complex constant due to limits
- on precision.</li>
-</ul>
-
-<p>
-These requirements apply both to literal constants and to the result
-of evaluating <a href="#Constant_expressions">constant
-expressions</a>.
-</p>
-
-
-<h2 id="Variables">Variables</h2>
-
-<p>
-A variable is a storage location for holding a <i>value</i>.
-The set of permissible values is determined by the
-variable's <i><a href="#Types">type</a></i>.
-</p>
-
-<p>
-A <a href="#Variable_declarations">variable declaration</a>
-or, for function parameters and results, the signature
-of a <a href="#Function_declarations">function declaration</a>
-or <a href="#Function_literals">function literal</a> reserves
-storage for a named variable.
-
-Calling the built-in function <a href="#Allocation"><code>new</code></a>
-or taking the address of a <a href="#Composite_literals">composite literal</a>
-allocates storage for a variable at run time.
-Such an anonymous variable is referred to via a (possibly implicit)
-<a href="#Address_operators">pointer indirection</a>.
-</p>
-
-<p>
-<i>Structured</i> variables of <a href="#Array_types">array</a>, <a href="#Slice_types">slice</a>,
-and <a href="#Struct_types">struct</a> types have elements and fields that may
-be <a href="#Address_operators">addressed</a> individually. Each such element
-acts like a variable.
-</p>
-
-<p>
-The <i>static type</i> (or just <i>type</i>) of a variable is the
-type given in its declaration, the type provided in the
-<code>new</code> call or composite literal, or the type of
-an element of a structured variable.
-Variables of interface type also have a distinct <i>dynamic type</i>,
-which is the (non-interface) type of the value assigned to the variable at run time
-(unless the value is the predeclared identifier <code>nil</code>,
-which has no type).
-The dynamic type may vary during execution but values stored in interface
-variables are always <a href="#Assignability">assignable</a>
-to the static type of the variable.
-</p>
-
-<pre>
-var x interface{} // x is nil and has static type interface{}
-var v *T // v has value nil, static type *T
-x = 42 // x has value 42 and dynamic type int
-x = v // x has value (*T)(nil) and dynamic type *T
-</pre>
-
-<p>
-A variable's value is retrieved by referring to the variable in an
-<a href="#Expressions">expression</a>; it is the most recent value
-<a href="#Assignments">assigned</a> to the variable.
-If a variable has not yet been assigned a value, its value is the
-<a href="#The_zero_value">zero value</a> for its type.
-</p>
-
-
-<h2 id="Types">Types</h2>
-
-<p>
-A type determines a set of values together with operations and methods specific
-to those values. A type may be denoted by a <i>type name</i>, if it has one, which must be
-followed by <a href="#Instantiations">type arguments</a> if the type is generic.
-A type may also be specified using a <i>type literal</i>, which composes a type
-from existing types.
-</p>
-
-<pre class="ebnf">
-Type = TypeName [ TypeArgs ] | TypeLit | "(" Type ")" .
-TypeName = identifier | QualifiedIdent .
-TypeArgs = "[" TypeList [ "," ] "]" .
-TypeList = Type { "," Type } .
-TypeLit = ArrayType | StructType | PointerType | FunctionType | InterfaceType |
- SliceType | MapType | ChannelType .
-</pre>
-
-<p>
-The language <a href="#Predeclared_identifiers">predeclares</a> certain type names.
-Others are introduced with <a href="#Type_declarations">type declarations</a>
-or <a href="#Type_parameter_declarations">type parameter lists</a>.
-<i>Composite types</i>—array, struct, pointer, function,
-interface, slice, map, and channel types—may be constructed using
-type literals.
-</p>
-
-<p>
-Predeclared types, defined types, and type parameters are called <i>named types</i>.
-An alias denotes a named type if the type given in the alias declaration is a named type.
-</p>
-
-<h3 id="Boolean_types">Boolean types</h3>
-
-<p>
-A <i>boolean type</i> represents the set of Boolean truth values
-denoted by the predeclared constants <code>true</code>
-and <code>false</code>. The predeclared boolean type is <code>bool</code>;
-it is a <a href="#Type_definitions">defined type</a>.
-</p>
-
-<h3 id="Numeric_types">Numeric types</h3>
-
-<p>
-An <i>integer</i>, <i>floating-point</i>, or <i>complex</i> type
-represents the set of integer, floating-point, or complex values, respectively.
-They are collectively called <i>numeric types</i>.
-The predeclared architecture-independent numeric types are:
-</p>
-
-<pre class="grammar">
-uint8 the set of all unsigned 8-bit integers (0 to 255)
-uint16 the set of all unsigned 16-bit integers (0 to 65535)
-uint32 the set of all unsigned 32-bit integers (0 to 4294967295)
-uint64 the set of all unsigned 64-bit integers (0 to 18446744073709551615)
-
-int8 the set of all signed 8-bit integers (-128 to 127)
-int16 the set of all signed 16-bit integers (-32768 to 32767)
-int32 the set of all signed 32-bit integers (-2147483648 to 2147483647)
-int64 the set of all signed 64-bit integers (-9223372036854775808 to 9223372036854775807)
-
-float32 the set of all IEEE-754 32-bit floating-point numbers
-float64 the set of all IEEE-754 64-bit floating-point numbers
-
-complex64 the set of all complex numbers with float32 real and imaginary parts
-complex128 the set of all complex numbers with float64 real and imaginary parts
-
-byte alias for uint8
-rune alias for int32
-</pre>
-
-<p>
-The value of an <i>n</i>-bit integer is <i>n</i> bits wide and represented using
-<a href="https://en.wikipedia.org/wiki/Two's_complement">two's complement arithmetic</a>.
-</p>
-
-<p>
-There is also a set of predeclared integer types with implementation-specific sizes:
-</p>
-
-<pre class="grammar">
-uint either 32 or 64 bits
-int same size as uint
-uintptr an unsigned integer large enough to store the uninterpreted bits of a pointer value
-</pre>
-
-<p>
-To avoid portability issues all numeric types are <a href="#Type_definitions">defined
-types</a> and thus distinct except
-<code>byte</code>, which is an <a href="#Alias_declarations">alias</a> for <code>uint8</code>, and
-<code>rune</code>, which is an alias for <code>int32</code>.
-Explicit conversions
-are required when different numeric types are mixed in an expression
-or assignment. For instance, <code>int32</code> and <code>int</code>
-are not the same type even though they may have the same size on a
-particular architecture.
-
-
-<h3 id="String_types">String types</h3>
-
-<p>
-A <i>string type</i> represents the set of string values.
-A string value is a (possibly empty) sequence of bytes.
-The number of bytes is called the length of the string and is never negative.
-Strings are immutable: once created,
-it is impossible to change the contents of a string.
-The predeclared string type is <code>string</code>;
-it is a <a href="#Type_definitions">defined type</a>.
-</p>
-
-<p>
-The length of a string <code>s</code> can be discovered using
-the built-in function <a href="#Length_and_capacity"><code>len</code></a>.
-The length is a compile-time constant if the string is a constant.
-A string's bytes can be accessed by integer <a href="#Index_expressions">indices</a>
-0 through <code>len(s)-1</code>.
-It is illegal to take the address of such an element; if
-<code>s[i]</code> is the <code>i</code>'th byte of a
-string, <code>&s[i]</code> is invalid.
-</p>
-
-
-<h3 id="Array_types">Array types</h3>
-
-<p>
-An array is a numbered sequence of elements of a single
-type, called the element type.
-The number of elements is called the length of the array and is never negative.
-</p>
-
-<pre class="ebnf">
-ArrayType = "[" ArrayLength "]" ElementType .
-ArrayLength = Expression .
-ElementType = Type .
-</pre>
-
-<p>
-The length is part of the array's type; it must evaluate to a
-non-negative <a href="#Constants">constant</a>
-<a href="#Representability">representable</a> by a value
-of type <code>int</code>.
-The length of array <code>a</code> can be discovered
-using the built-in function <a href="#Length_and_capacity"><code>len</code></a>.
-The elements can be addressed by integer <a href="#Index_expressions">indices</a>
-0 through <code>len(a)-1</code>.
-Array types are always one-dimensional but may be composed to form
-multi-dimensional types.
-</p>
-
-<pre>
-[32]byte
-[2*N] struct { x, y int32 }
-[1000]*float64
-[3][5]int
-[2][2][2]float64 // same as [2]([2]([2]float64))
-</pre>
-
-<h3 id="Slice_types">Slice types</h3>
-
-<p>
-A slice is a descriptor for a contiguous segment of an <i>underlying array</i> and
-provides access to a numbered sequence of elements from that array.
-A slice type denotes the set of all slices of arrays of its element type.
-The number of elements is called the length of the slice and is never negative.
-The value of an uninitialized slice is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-SliceType = "[" "]" ElementType .
-</pre>
-
-<p>
-The length of a slice <code>s</code> can be discovered by the built-in function
-<a href="#Length_and_capacity"><code>len</code></a>; unlike with arrays it may change during
-execution. The elements can be addressed by integer <a href="#Index_expressions">indices</a>
-0 through <code>len(s)-1</code>. The slice index of a
-given element may be less than the index of the same element in the
-underlying array.
-</p>
-<p>
-A slice, once initialized, is always associated with an underlying
-array that holds its elements. A slice therefore shares storage
-with its array and with other slices of the same array; by contrast,
-distinct arrays always represent distinct storage.
-</p>
-<p>
-The array underlying a slice may extend past the end of the slice.
-The <i>capacity</i> is a measure of that extent: it is the sum of
-the length of the slice and the length of the array beyond the slice;
-a slice of length up to that capacity can be created by
-<a href="#Slice_expressions"><i>slicing</i></a> a new one from the original slice.
-The capacity of a slice <code>a</code> can be discovered using the
-built-in function <a href="#Length_and_capacity"><code>cap(a)</code></a>.
-</p>
-
-<p>
-A new, initialized slice value for a given element type <code>T</code> may be
-made using the built-in function
-<a href="#Making_slices_maps_and_channels"><code>make</code></a>,
-which takes a slice type
-and parameters specifying the length and optionally the capacity.
-A slice created with <code>make</code> always allocates a new, hidden array
-to which the returned slice value refers. That is, executing
-</p>
-
-<pre>
-make([]T, length, capacity)
-</pre>
-
-<p>
-produces the same slice as allocating an array and <a href="#Slice_expressions">slicing</a>
-it, so these two expressions are equivalent:
-</p>
-
-<pre>
-make([]int, 50, 100)
-new([100]int)[0:50]
-</pre>
-
-<p>
-Like arrays, slices are always one-dimensional but may be composed to construct
-higher-dimensional objects.
-With arrays of arrays, the inner arrays are, by construction, always the same length;
-however with slices of slices (or arrays of slices), the inner lengths may vary dynamically.
-Moreover, the inner slices must be initialized individually.
-</p>
-
-<h3 id="Struct_types">Struct types</h3>
-
-<p>
-A struct is a sequence of named elements, called fields, each of which has a
-name and a type. Field names may be specified explicitly (IdentifierList) or
-implicitly (EmbeddedField).
-Within a struct, non-<a href="#Blank_identifier">blank</a> field names must
-be <a href="#Uniqueness_of_identifiers">unique</a>.
-</p>
-
-<pre class="ebnf">
-StructType = "struct" "{" { FieldDecl ";" } "}" .
-FieldDecl = (IdentifierList Type | EmbeddedField) [ Tag ] .
-EmbeddedField = [ "*" ] TypeName .
-Tag = string_lit .
-</pre>
-
-<pre>
-// An empty struct.
-struct {}
-
-// A struct with 6 fields.
-struct {
- x, y int
- u float32
- _ float32 // padding
- A *[]int
- F func()
-}
-</pre>
-
-<p>
-A field declared with a type but no explicit field name is called an <i>embedded field</i>.
-An embedded field must be specified as
-a type name <code>T</code> or as a pointer to a non-interface type name <code>*T</code>,
-and <code>T</code> itself may not be
-a pointer type. The unqualified type name acts as the field name.
-</p>
-
-<pre>
-// A struct with four embedded fields of types T1, *T2, P.T3 and *P.T4
-struct {
- T1 // field name is T1
- *T2 // field name is T2
- P.T3 // field name is T3
- *P.T4 // field name is T4
- x, y int // field names are x and y
-}
-</pre>
-
-<p>
-The following declaration is illegal because field names must be unique
-in a struct type:
-</p>
-
-<pre>
-struct {
- T // conflicts with embedded field *T and *P.T
- *T // conflicts with embedded field T and *P.T
- *P.T // conflicts with embedded field T and *T
-}
-</pre>
-
-<p>
-A field or <a href="#Method_declarations">method</a> <code>f</code> of an
-embedded field in a struct <code>x</code> is called <i>promoted</i> if
-<code>x.f</code> is a legal <a href="#Selectors">selector</a> that denotes
-that field or method <code>f</code>.
-</p>
-
-<p>
-Promoted fields act like ordinary fields
-of a struct except that they cannot be used as field names in
-<a href="#Composite_literals">composite literals</a> of the struct.
-</p>
-
-<p>
-Given a struct type <code>S</code> and a <a href="#Type_definitions">defined type</a>
-<code>T</code>, promoted methods are included in the method set of the struct as follows:
-</p>
-<ul>
- <li>
- If <code>S</code> contains an embedded field <code>T</code>,
- the <a href="#Method_sets">method sets</a> of <code>S</code>
- and <code>*S</code> both include promoted methods with receiver
- <code>T</code>. The method set of <code>*S</code> also
- includes promoted methods with receiver <code>*T</code>.
- </li>
-
- <li>
- If <code>S</code> contains an embedded field <code>*T</code>,
- the method sets of <code>S</code> and <code>*S</code> both
- include promoted methods with receiver <code>T</code> or
- <code>*T</code>.
- </li>
-</ul>
-
-<p>
-A field declaration may be followed by an optional string literal <i>tag</i>,
-which becomes an attribute for all the fields in the corresponding
-field declaration. An empty tag string is equivalent to an absent tag.
-The tags are made visible through a <a href="/pkg/reflect/#StructTag">reflection interface</a>
-and take part in <a href="#Type_identity">type identity</a> for structs
-but are otherwise ignored.
-</p>
-
-<pre>
-struct {
- x, y float64 "" // an empty tag string is like an absent tag
- name string "any string is permitted as a tag"
- _ [4]byte "ceci n'est pas un champ de structure"
-}
-
-// A struct corresponding to a TimeStamp protocol buffer.
-// The tag strings define the protocol buffer field numbers;
-// they follow the convention outlined by the reflect package.
-struct {
- microsec uint64 `protobuf:"1"`
- serverIP6 uint64 `protobuf:"2"`
-}
-</pre>
-
-<h3 id="Pointer_types">Pointer types</h3>
-
-<p>
-A pointer type denotes the set of all pointers to <a href="#Variables">variables</a> of a given
-type, called the <i>base type</i> of the pointer.
-The value of an uninitialized pointer is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-PointerType = "*" BaseType .
-BaseType = Type .
-</pre>
-
-<pre>
-*Point
-*[4]int
-</pre>
-
-<h3 id="Function_types">Function types</h3>
-
-<p>
-A function type denotes the set of all functions with the same parameter
-and result types. The value of an uninitialized variable of function type
-is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-FunctionType = "func" Signature .
-Signature = Parameters [ Result ] .
-Result = Parameters | Type .
-Parameters = "(" [ ParameterList [ "," ] ] ")" .
-ParameterList = ParameterDecl { "," ParameterDecl } .
-ParameterDecl = [ IdentifierList ] [ "..." ] Type .
-</pre>
-
-<p>
-Within a list of parameters or results, the names (IdentifierList)
-must either all be present or all be absent. If present, each name
-stands for one item (parameter or result) of the specified type and
-all non-<a href="#Blank_identifier">blank</a> names in the signature
-must be <a href="#Uniqueness_of_identifiers">unique</a>.
-If absent, each type stands for one item of that type.
-Parameter and result
-lists are always parenthesized except that if there is exactly
-one unnamed result it may be written as an unparenthesized type.
-</p>
-
-<p>
-The final incoming parameter in a function signature may have
-a type prefixed with <code>...</code>.
-A function with such a parameter is called <i>variadic</i> and
-may be invoked with zero or more arguments for that parameter.
-</p>
-
-<pre>
-func()
-func(x int) int
-func(a, _ int, z float32) bool
-func(a, b int, z float32) (bool)
-func(prefix string, values ...int)
-func(a, b int, z float64, opt ...interface{}) (success bool)
-func(int, int, float64) (float64, *[]int)
-func(n int) func(p *T)
-</pre>
-
-<h3 id="Interface_types">Interface types</h3>
-
-<p>
-An interface type defines a <i>type set</i>.
-A variable of interface type can store a value of any type that is in the type
-set of the interface. Such a type is said to
-<a href="#Implementing_an_interface">implement the interface</a>.
-The value of an uninitialized variable of interface type is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-InterfaceType = "interface" "{" { InterfaceElem ";" } "}" .
-InterfaceElem = MethodElem | TypeElem .
-MethodElem = MethodName Signature .
-MethodName = identifier .
-TypeElem = TypeTerm { "|" TypeTerm } .
-TypeTerm = Type | UnderlyingType .
-UnderlyingType = "~" Type .
-</pre>
-
-<p>
-An interface type is specified by a list of <i>interface elements</i>.
-An interface element is either a <i>method</i> or a <i>type element</i>,
-where a type element is a union of one or more <i>type terms</i>.
-A type term is either a single type or a single underlying type.
-</p>
-
-<h4 id="Basic_interfaces">Basic interfaces</h4>
-
-<p>
-In its most basic form an interface specifies a (possibly empty) list of methods.
-The type set defined by such an interface is the set of types which implement all of
-those methods, and the corresponding <a href="#Method_sets">method set</a> consists
-exactly of the methods specified by the interface.
-Interfaces whose type sets can be defined entirely by a list of methods are called
-<i>basic interfaces.</i>
-</p>
-
-<pre>
-// A simple File interface.
-interface {
- Read([]byte) (int, error)
- Write([]byte) (int, error)
- Close() error
-}
-</pre>
-
-<p>
-The name of each explicitly specified method must be <a href="#Uniqueness_of_identifiers">unique</a>
-and not <a href="#Blank_identifier">blank</a>.
-</p>
-
-<pre>
-interface {
- String() string
- String() string // illegal: String not unique
- _(x int) // illegal: method must have non-blank name
-}
-</pre>
-
-<p>
-More than one type may implement an interface.
-For instance, if two types <code>S1</code> and <code>S2</code>
-have the method set
-</p>
-
-<pre>
-func (p T) Read(p []byte) (n int, err error)
-func (p T) Write(p []byte) (n int, err error)
-func (p T) Close() error
-</pre>
-
-<p>
-(where <code>T</code> stands for either <code>S1</code> or <code>S2</code>)
-then the <code>File</code> interface is implemented by both <code>S1</code> and
-<code>S2</code>, regardless of what other methods
-<code>S1</code> and <code>S2</code> may have or share.
-</p>
-
-<p>
-Every type that is a member of the type set of an interface implements that interface.
-Any given type may implement several distinct interfaces.
-For instance, all types implement the <i>empty interface</i> which stands for the set of all types:
-</p>
-
-<pre>
-interface{}
-</pre>
-
-<p>
-For convenience, the predeclared type <code>any</code> is an alias for the empty interface.
-</p>
-
-<p>
-Similarly, consider this interface specification,
-which appears within a <a href="#Type_declarations">type declaration</a>
-to define an interface called <code>Locker</code>:
-</p>
-
-<pre>
-type Locker interface {
- Lock()
- Unlock()
-}
-</pre>
-
-<p>
-If <code>S1</code> and <code>S2</code> also implement
-</p>
-
-<pre>
-func (p T) Lock() { … }
-func (p T) Unlock() { … }
-</pre>
-
-<p>
-they implement the <code>Locker</code> interface as well
-as the <code>File</code> interface.
-</p>
-
-<h4 id="Embedded_interfaces">Embedded interfaces</h4>
-
-<p>
-In a slightly more general form
-an interface <code>T</code> may use a (possibly qualified) interface type
-name <code>E</code> as an interface element. This is called
-<i>embedding</i> interface <code>E</code> in <code>T</code>.
-The type set of <code>T</code> is the <i>intersection</i> of the type sets
-defined by <code>T</code>'s explicitly declared methods and the type sets
-of <code>T</code>’s embedded interfaces.
-In other words, the type set of <code>T</code> is the set of all types that implement all the
-explicitly declared methods of <code>T</code> and also all the methods of
-<code>E</code>.
-</p>
-
-<pre>
-type Reader interface {
- Read(p []byte) (n int, err error)
- Close() error
-}
-
-type Writer interface {
- Write(p []byte) (n int, err error)
- Close() error
-}
-
-// ReadWriter's methods are Read, Write, and Close.
-type ReadWriter interface {
- Reader // includes methods of Reader in ReadWriter's method set
- Writer // includes methods of Writer in ReadWriter's method set
-}
-</pre>
-
-<p>
-When embedding interfaces, methods with the
-<a href="#Uniqueness_of_identifiers">same</a> names must
-have <a href="#Type_identity">identical</a> signatures.
-</p>
-
-<pre>
-type ReadCloser interface {
- Reader // includes methods of Reader in ReadCloser's method set
- Close() // illegal: signatures of Reader.Close and Close are different
-}
-</pre>
-
-<h4 id="General_interfaces">General interfaces</h4>
-
-<p>
-In their most general form, an interface element may also be an arbitrary type term
-<code>T</code>, or a term of the form <code>~T</code> specifying the underlying type <code>T</code>,
-or a union of terms <code>t<sub>1</sub>|t<sub>2</sub>|…|t<sub>n</sub></code>.
-Together with method specifications, these elements enable the precise
-definition of an interface's type set as follows:
-</p>
-
-<ul>
- <li>The type set of the empty interface is the set of all non-interface types.
- </li>
-
- <li>The type set of a non-empty interface is the intersection of the type sets
- of its interface elements.
- </li>
-
- <li>The type set of a method specification is the set of types
- whose method sets include that method.
- </li>
-
- <li>The type set of a non-interface type term is the set consisting
- of just that type.
- </li>
-
- <li>The type set of a term of the form <code>~T</code>
- is the set of types whose underlying type is <code>T</code>.
- </li>
-
- <li>The type set of a <i>union</i> of terms
- <code>t<sub>1</sub>|t<sub>2</sub>|…|t<sub>n</sub></code>
- is the union of the type sets of the terms.
- </li>
-</ul>
-
-<p>
-By construction, an interface's type set never contains an interface type.
-</p>
-
-<pre>
-// An interface representing only the type int.
-interface {
- int
-}
-
-// An interface representing all types with underlying type int.
-interface {
- ~int
-}
-
-// An interface representing all types with underlying type int that implement the String method.
-interface {
- ~int
- String() string
-}
-
-// An interface representing an empty type set: there is no type that is both an int and a string.
-interface {
- int
- string
-}
-</pre>
-
-<p>
-In a term of the form <code>~T</code>, the underlying type of <code>T</code>
-must be itself, and <code>T</code> cannot be an interface.
-</p>
-
-<pre>
-type MyInt int
-
-interface {
- ~[]byte // the underlying type of []byte is itself
- ~MyInt // illegal: the underlying type of MyInt is not MyInt
- ~error // illegal: error is an interface
-}
-</pre>
-
-<p>
-Union elements denote unions of type sets:
-</p>
-
-<pre>
-// The Float interface represents all floating-point types
-// (including any named types whose underlying types are
-// either float32 or float64).
-type Float interface {
- ~float32 | ~float64
-}
-</pre>
-
-<p>
-In a union, a term cannot be a <a href="#Type_parameter_declarations">type parameter</a>, and the type sets of all
-non-interface terms must be pairwise disjoint (the pairwise intersection of the type sets must be empty).
-Given a type parameter <code>P</code>:
-</p>
-
-<pre>
-interface {
- P // illegal: P is a type parameter
- int | P // illegal: P is a type parameter
- ~int | MyInt // illegal: the type sets for ~int and MyInt are not disjoint (~int includes MyInt)
- float32 | Float // overlapping type sets but Float is an interface
-}
-</pre>
-
-<p>
-Implementation restriction:
-A union (with more than one term) cannot contain the
-<a href="#Predeclared_identifiers">predeclared identifier</a> <code>comparable</code>
-or interfaces that specify methods, or embed <code>comparable</code> or interfaces
-that specify methods.
-</p>
-
-<p>
-Interfaces that are not <a href="#Basic_interfaces">basic</a> may only be used as type
-constraints, or as elements of other interfaces used as constraints.
-They cannot be the types of values or variables, or components of other,
-non-interface types.
-</p>
-
-<pre>
-var x Float // illegal: Float is not a basic interface
-
-var x interface{} = Float(nil) // illegal
-
-type Floatish struct {
- f Float // illegal
-}
-</pre>
-
-<p>
-An interface type <code>T</code> may not embed any type element
-that is, contains, or embeds <code>T</code>, recursively.
-</p>
-
-<pre>
-// illegal: Bad cannot embed itself
-type Bad interface {
- Bad
-}
-
-// illegal: Bad1 cannot embed itself using Bad2
-type Bad1 interface {
- Bad2
-}
-type Bad2 interface {
- Bad1
-}
-
-// illegal: Bad3 cannot embed a union containing Bad3
-type Bad3 interface {
- ~int | ~string | Bad3
-}
-</pre>
-
-<h4 id="Implementing_an_interface">Implementing an interface</h4>
-
-<p>
-A type <code>T</code> implements an interface <code>I</code> if
-</p>
-
-<ul>
-<li>
- <code>T</code> is not an interface and is an element of the type set of <code>I</code>; or
-</li>
-<li>
- <code>T</code> is an interface and the type set of <code>T</code> is a subset of the
- type set of <code>I</code>.
-</li>
-</ul>
-
-<p>
-A value of type <code>T</code> implements an interface if <code>T</code>
-implements the interface.
-</p>
-
-<h3 id="Map_types">Map types</h3>
-
-<p>
-A map is an unordered group of elements of one type, called the
-element type, indexed by a set of unique <i>keys</i> of another type,
-called the key type.
-The value of an uninitialized map is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-MapType = "map" "[" KeyType "]" ElementType .
-KeyType = Type .
-</pre>
-
-<p>
-The <a href="#Comparison_operators">comparison operators</a>
-<code>==</code> and <code>!=</code> must be fully defined
-for operands of the key type; thus the key type must not be a function, map, or
-slice.
-If the key type is an interface type, these
-comparison operators must be defined for the dynamic key values;
-failure will cause a <a href="#Run_time_panics">run-time panic</a>.
-</p>
-
-<pre>
-map[string]int
-map[*T]struct{ x, y float64 }
-map[string]interface{}
-</pre>
-
-<p>
-The number of map elements is called its length.
-For a map <code>m</code>, it can be discovered using the
-built-in function <a href="#Length_and_capacity"><code>len</code></a>
-and may change during execution. Elements may be added during execution
-using <a href="#Assignments">assignments</a> and retrieved with
-<a href="#Index_expressions">index expressions</a>; they may be removed with the
-<a href="#Deletion_of_map_elements"><code>delete</code></a> built-in function.
-</p>
-<p>
-A new, empty map value is made using the built-in
-function <a href="#Making_slices_maps_and_channels"><code>make</code></a>,
-which takes the map type and an optional capacity hint as arguments:
-</p>
-
-<pre>
-make(map[string]int)
-make(map[string]int, 100)
-</pre>
-
-<p>
-The initial capacity does not bound its size:
-maps grow to accommodate the number of items
-stored in them, with the exception of <code>nil</code> maps.
-A <code>nil</code> map is equivalent to an empty map except that no elements
-may be added.
-
-<h3 id="Channel_types">Channel types</h3>
-
-<p>
-A channel provides a mechanism for
-<a href="#Go_statements">concurrently executing functions</a>
-to communicate by
-<a href="#Send_statements">sending</a> and
-<a href="#Receive_operator">receiving</a>
-values of a specified element type.
-The value of an uninitialized channel is <code>nil</code>.
-</p>
-
-<pre class="ebnf">
-ChannelType = ( "chan" | "chan" "<-" | "<-" "chan" ) ElementType .
-</pre>
-
-<p>
-The optional <code><-</code> operator specifies the channel <i>direction</i>,
-<i>send</i> or <i>receive</i>. If a direction is given, the channel is <i>directional</i>,
-otherwise it is <i>bidirectional</i>.
-A channel may be constrained only to send or only to receive by
-<a href="#Assignments">assignment</a> or
-explicit <a href="#Conversions">conversion</a>.
-</p>
-
-<pre>
-chan T // can be used to send and receive values of type T
-chan<- float64 // can only be used to send float64s
-<-chan int // can only be used to receive ints
-</pre>
-
-<p>
-The <code><-</code> operator associates with the leftmost <code>chan</code>
-possible:
-</p>
-
-<pre>
-chan<- chan int // same as chan<- (chan int)
-chan<- <-chan int // same as chan<- (<-chan int)
-<-chan <-chan int // same as <-chan (<-chan int)
-chan (<-chan int)
-</pre>
-
-<p>
-A new, initialized channel
-value can be made using the built-in function
-<a href="#Making_slices_maps_and_channels"><code>make</code></a>,
-which takes the channel type and an optional <i>capacity</i> as arguments:
-</p>
-
-<pre>
-make(chan int, 100)
-</pre>
-
-<p>
-The capacity, in number of elements, sets the size of the buffer in the channel.
-If the capacity is zero or absent, the channel is unbuffered and communication
-succeeds only when both a sender and receiver are ready. Otherwise, the channel
-is buffered and communication succeeds without blocking if the buffer
-is not full (sends) or not empty (receives).
-A <code>nil</code> channel is never ready for communication.
-</p>
-
-<p>
-A channel may be closed with the built-in function
-<a href="#Close"><code>close</code></a>.
-The multi-valued assignment form of the
-<a href="#Receive_operator">receive operator</a>
-reports whether a received value was sent before
-the channel was closed.
-</p>
-
-<p>
-A single channel may be used in
-<a href="#Send_statements">send statements</a>,
-<a href="#Receive_operator">receive operations</a>,
-and calls to the built-in functions
-<a href="#Length_and_capacity"><code>cap</code></a> and
-<a href="#Length_and_capacity"><code>len</code></a>
-by any number of goroutines without further synchronization.
-Channels act as first-in-first-out queues.
-For example, if one goroutine sends values on a channel
-and a second goroutine receives them, the values are
-received in the order sent.
-</p>
-
-<h2 id="Properties_of_types_and_values">Properties of types and values</h2>
-
-<h3 id="Underlying_types">Underlying types</h3>
-
-<p>
-Each type <code>T</code> has an <i>underlying type</i>: If <code>T</code>
-is one of the predeclared boolean, numeric, or string types, or a type literal,
-the corresponding underlying type is <code>T</code> itself.
-Otherwise, <code>T</code>'s underlying type is the underlying type of the
-type to which <code>T</code> refers in its declaration.
-For a type parameter that is the underlying type of its
-<a href="#Type_constraints">type constraint</a>, which is always an interface.
-</p>
-
-<pre>
-type (
- A1 = string
- A2 = A1
-)
-
-type (
- B1 string
- B2 B1
- B3 []B1
- B4 B3
-)
-
-func f[P any](x P) { … }
-</pre>
-
-<p>
-The underlying type of <code>string</code>, <code>A1</code>, <code>A2</code>, <code>B1</code>,
-and <code>B2</code> is <code>string</code>.
-The underlying type of <code>[]B1</code>, <code>B3</code>, and <code>B4</code> is <code>[]B1</code>.
-The underlying type of <code>P</code> is <code>interface{}</code>.
-</p>
-
-<h3 id="Core_types">Core types</h3>
-
-<p>
-Each non-interface type <code>T</code> has a <i>core type</i>, which is the same as the
-<a href="#Underlying_types">underlying type</a> of <code>T</code>.
-</p>
-
-<p>
-An interface <code>T</code> has a core type if one of the following
-conditions is satisfied:
-</p>
-
-<ol>
-<li>
-There is a single type <code>U</code> which is the <a href="#Underlying_types">underlying type</a>
-of all types in the <a href="#Interface_types">type set</a> of <code>T</code>; or
-</li>
-<li>
-the type set of <code>T</code> contains only <a href="#Channel_types">channel types</a>
-with identical element type <code>E</code>, and all directional channels have the same
-direction.
-</li>
-</ol>
-
-<p>
-No other interfaces have a core type.
-</p>
-
-<p>
-The core type of an interface is, depending on the condition that is satisfied, either:
-</p>
-
-<ol>
-<li>
-the type <code>U</code>; or
-</li>
-<li>
-the type <code>chan E</code> if <code>T</code> contains only bidirectional
-channels, or the type <code>chan<- E</code> or <code><-chan E</code>
-depending on the direction of the directional channels present.
-</li>
-</ol>
-
-<p>
-By definition, a core type is never a <a href="#Type_definitions">defined type</a>,
-<a href="#Type_parameter_declarations">type parameter</a>, or
-<a href="#Interface_types">interface type</a>.
-</p>
-
-<p>
-Examples of interfaces with core types:
-</p>
-
-<pre>
-type Celsius float32
-type Kelvin float32
-
-interface{ int } // int
-interface{ Celsius|Kelvin } // float32
-interface{ ~chan int } // chan int
-interface{ ~chan int|~chan<- int } // chan<- int
-interface{ ~[]*data; String() string } // []*data
-</pre>
-
-<p>
-Examples of interfaces without core types:
-</p>
-
-<pre>
-interface{} // no single underlying type
-interface{ Celsius|float64 } // no single underlying type
-interface{ chan int | chan<- string } // channels have different element types
-interface{ <-chan int | chan<- int } // directional channels have different directions
-</pre>
-
-<h3 id="Type_identity">Type identity</h3>
-
-<p>
-Two types are either <i>identical</i> or <i>different</i>.
-</p>
-
-<p>
-A <a href="#Types">named type</a> is always different from any other type.
-Otherwise, two types are identical if their <a href="#Types">underlying</a> type literals are
-structurally equivalent; that is, they have the same literal structure and corresponding
-components have identical types. In detail:
-</p>
-
-<ul>
- <li>Two array types are identical if they have identical element types and
- the same array length.</li>
-
- <li>Two slice types are identical if they have identical element types.</li>
-
- <li>Two struct types are identical if they have the same sequence of fields,
- and if corresponding fields have the same names, and identical types,
- and identical tags.
- <a href="#Exported_identifiers">Non-exported</a> field names from different
- packages are always different.</li>
-
- <li>Two pointer types are identical if they have identical base types.</li>
-
- <li>Two function types are identical if they have the same number of parameters
- and result values, corresponding parameter and result types are
- identical, and either both functions are variadic or neither is.
- Parameter and result names are not required to match.</li>
-
- <li>Two interface types are identical if they define the same type set.
- </li>
-
- <li>Two map types are identical if they have identical key and element types.</li>
-
- <li>Two channel types are identical if they have identical element types and
- the same direction.</li>
-
- <li>Two <a href="#Instantiations">instantiated</a> types are identical if
- their defined types and all type arguments are identical.
- </li>
-</ul>
-
-<p>
-Given the declarations
-</p>
-
-<pre>
-type (
- A0 = []string
- A1 = A0
- A2 = struct{ a, b int }
- A3 = int
- A4 = func(A3, float64) *A0
- A5 = func(x int, _ float64) *[]string
-
- B0 A0
- B1 []string
- B2 struct{ a, b int }
- B3 struct{ a, c int }
- B4 func(int, float64) *B0
- B5 func(x int, y float64) *A1
-
- C0 = B0
- D0[P1, P2 any] struct{ x P1; y P2 }
- E0 = D0[int, string]
-)
-</pre>
-
-<p>
-these types are identical:
-</p>
-
-<pre>
-A0, A1, and []string
-A2 and struct{ a, b int }
-A3 and int
-A4, func(int, float64) *[]string, and A5
-
-B0 and C0
-D0[int, string] and E0
-[]int and []int
-struct{ a, b *T5 } and struct{ a, b *T5 }
-func(x int, y float64) *[]string, func(int, float64) (result *[]string), and A5
-</pre>
-
-<p>
-<code>B0</code> and <code>B1</code> are different because they are new types
-created by distinct <a href="#Type_definitions">type definitions</a>;
-<code>func(int, float64) *B0</code> and <code>func(x int, y float64) *[]string</code>
-are different because <code>B0</code> is different from <code>[]string</code>;
-and <code>P1</code> and <code>P2</code> are different because they are different
-type parameters.
-<code>D0[int, string]</code> and <code>struct{ x int; y string }</code> are
-different because the former is an <a href="#Instantiations">instantiated</a>
-defined type while the latter is a type literal
-(but they are still <a href="#Assignability">assignable</a>).
-</p>
-
-<h3 id="Assignability">Assignability</h3>
-
-<p>
-A value <code>x</code> of type <code>V</code> is <i>assignable</i> to a <a href="#Variables">variable</a> of type <code>T</code>
-("<code>x</code> is assignable to <code>T</code>") if one of the following conditions applies:
-</p>
-
-<ul>
-<li>
-<code>V</code> and <code>T</code> are identical.
-</li>
-<li>
-<code>V</code> and <code>T</code> have identical
-<a href="#Underlying_types">underlying types</a> and at least one of <code>V</code>
-or <code>T</code> is not a <a href="#Types">named type</a>.
-</li>
-<li>
-<code>V</code> and <code>T</code> are channel types with
-identical element types, <code>V</code> is a bidirectional channel,
-and at least one of <code>V</code> or <code>T</code> is not a <a href="#Types">named type</a>.
-</li>
-<li>
-<code>T</code> is an interface type, but not a type parameter, and
-<code>x</code> <a href="#Implementing_an_interface">implements</a> <code>T</code>.
-</li>
-<li>
-<code>x</code> is the predeclared identifier <code>nil</code> and <code>T</code>
-is a pointer, function, slice, map, channel, or interface type,
-but not a type parameter.
-</li>
-<li>
-<code>x</code> is an untyped <a href="#Constants">constant</a>
-<a href="#Representability">representable</a>
-by a value of type <code>T</code>.
-</li>
-</ul>
-
-<p>
-Additionally, if <code>x</code>'s type <code>V</code> or <code>T</code> are type parameters, <code>x</code>
-is assignable to a variable of type <code>T</code> if one of the following conditions applies:
-</p>
-
-<ul>
-<li>
-<code>x</code> is the predeclared identifier <code>nil</code>, <code>T</code> is
-a type parameter, and <code>x</code> is assignable to each type in
-<code>T</code>'s type set.
-</li>
-<li>
-<code>V</code> is not a <a href="#Types">named type</a>, <code>T</code> is
-a type parameter, and <code>x</code> is assignable to each type in
-<code>T</code>'s type set.
-</li>
-<li>
-<code>V</code> is a type parameter and <code>T</code> is not a named type,
-and values of each type in <code>V</code>'s type set are assignable
-to <code>T</code>.
-</li>
-</ul>
-
-<h3 id="Representability">Representability</h3>
-
-<p>
-A <a href="#Constants">constant</a> <code>x</code> is <i>representable</i>
-by a value of type <code>T</code>,
-where <code>T</code> is not a <a href="#Type_parameter_declarations">type parameter</a>,
-if one of the following conditions applies:
-</p>
-
-<ul>
-<li>
-<code>x</code> is in the set of values <a href="#Types">determined</a> by <code>T</code>.
-</li>
-
-<li>
-<code>T</code> is a <a href="#Numeric_types">floating-point type</a> and <code>x</code> can be rounded to <code>T</code>'s
-precision without overflow. Rounding uses IEEE 754 round-to-even rules but with an IEEE
-negative zero further simplified to an unsigned zero. Note that constant values never result
-in an IEEE negative zero, NaN, or infinity.
-</li>
-
-<li>
-<code>T</code> is a complex type, and <code>x</code>'s
-<a href="#Complex_numbers">components</a> <code>real(x)</code> and <code>imag(x)</code>
-are representable by values of <code>T</code>'s component type (<code>float32</code> or
-<code>float64</code>).
-</li>
-</ul>
-
-<p>
-If <code>T</code> is a type parameter,
-<code>x</code> is representable by a value of type <code>T</code> if <code>x</code> is representable
-by a value of each type in <code>T</code>'s type set.
-</p>
-
-<pre>
-x T x is representable by a value of T because
-
-'a' byte 97 is in the set of byte values
-97 rune rune is an alias for int32, and 97 is in the set of 32-bit integers
-"foo" string "foo" is in the set of string values
-1024 int16 1024 is in the set of 16-bit integers
-42.0 byte 42 is in the set of unsigned 8-bit integers
-1e10 uint64 10000000000 is in the set of unsigned 64-bit integers
-2.718281828459045 float32 2.718281828459045 rounds to 2.7182817 which is in the set of float32 values
--1e-1000 float64 -1e-1000 rounds to IEEE -0.0 which is further simplified to 0.0
-0i int 0 is an integer value
-(42 + 0i) float32 42.0 (with zero imaginary part) is in the set of float32 values
-</pre>
-
-<pre>
-x T x is not representable by a value of T because
-
-0 bool 0 is not in the set of boolean values
-'a' string 'a' is a rune, it is not in the set of string values
-1024 byte 1024 is not in the set of unsigned 8-bit integers
--1 uint16 -1 is not in the set of unsigned 16-bit integers
-1.1 int 1.1 is not an integer value
-42i float32 (0 + 42i) is not in the set of float32 values
-1e1000 float64 1e1000 overflows to IEEE +Inf after rounding
-</pre>
-
-<h3 id="Method_sets">Method sets</h3>
-
-<p>
-The <i>method set</i> of a type determines the methods that can be
-<a href="#Calls">called</a> on an <a href="#Operands">operand</a> of that type.
-Every type has a (possibly empty) method set associated with it:
-</p>
-
-<ul>
-<li>The method set of a <a href="#Type_definitions">defined type</a> <code>T</code> consists of all
-<a href="#Method_declarations">methods</a> declared with receiver type <code>T</code>.
-</li>
-
-<li>
-The method set of a pointer to a defined type <code>T</code>
-(where <code>T</code> is neither a pointer nor an interface)
-is the set of all methods declared with receiver <code>*T</code> or <code>T</code>.
-</li>
-
-<li>The method set of an <a href="#Interface_types">interface type</a> is the intersection
-of the method sets of each type in the interface's <a href="#Interface_types">type set</a>
-(the resulting method set is usually just the set of declared methods in the interface).
-</li>
-</ul>
-
-<p>
-Further rules apply to structs (and pointer to structs) containing embedded fields,
-as described in the section on <a href="#Struct_types">struct types</a>.
-Any other type has an empty method set.
-</p>
-
-<p>
-In a method set, each method must have a
-<a href="#Uniqueness_of_identifiers">unique</a>
-non-<a href="#Blank_identifier">blank</a> <a href="#MethodName">method name</a>.
-</p>
-
-<h2 id="Blocks">Blocks</h2>
-
-<p>
-A <i>block</i> is a possibly empty sequence of declarations and statements
-within matching brace brackets.
-</p>
-
-<pre class="ebnf">
-Block = "{" StatementList "}" .
-StatementList = { Statement ";" } .
-</pre>
-
-<p>
-In addition to explicit blocks in the source code, there are implicit blocks:
-</p>
-
-<ol>
- <li>The <i>universe block</i> encompasses all Go source text.</li>
-
- <li>Each <a href="#Packages">package</a> has a <i>package block</i> containing all
- Go source text for that package.</li>
-
- <li>Each file has a <i>file block</i> containing all Go source text
- in that file.</li>
-
- <li>Each <a href="#If_statements">"if"</a>,
- <a href="#For_statements">"for"</a>, and
- <a href="#Switch_statements">"switch"</a>
- statement is considered to be in its own implicit block.</li>
-
- <li>Each clause in a <a href="#Switch_statements">"switch"</a>
- or <a href="#Select_statements">"select"</a> statement
- acts as an implicit block.</li>
-</ol>
-
-<p>
-Blocks nest and influence <a href="#Declarations_and_scope">scoping</a>.
-</p>
-
-
-<h2 id="Declarations_and_scope">Declarations and scope</h2>
-
-<p>
-A <i>declaration</i> binds a non-<a href="#Blank_identifier">blank</a> identifier to a
-<a href="#Constant_declarations">constant</a>,
-<a href="#Type_declarations">type</a>,
-<a href="#Type_parameter_declarations">type parameter</a>,
-<a href="#Variable_declarations">variable</a>,
-<a href="#Function_declarations">function</a>,
-<a href="#Labeled_statements">label</a>, or
-<a href="#Import_declarations">package</a>.
-Every identifier in a program must be declared.
-No identifier may be declared twice in the same block, and
-no identifier may be declared in both the file and package block.
-</p>
-
-<p>
-The <a href="#Blank_identifier">blank identifier</a> may be used like any other identifier
-in a declaration, but it does not introduce a binding and thus is not declared.
-In the package block, the identifier <code>init</code> may only be used for
-<a href="#Package_initialization"><code>init</code> function</a> declarations,
-and like the blank identifier it does not introduce a new binding.
-</p>
-
-<pre class="ebnf">
-Declaration = ConstDecl | TypeDecl | VarDecl .
-TopLevelDecl = Declaration | FunctionDecl | MethodDecl .
-</pre>
-
-<p>
-The <i>scope</i> of a declared identifier is the extent of source text in which
-the identifier denotes the specified constant, type, variable, function, label, or package.
-</p>
-
-<p>
-Go is lexically scoped using <a href="#Blocks">blocks</a>:
-</p>
-
-<ol>
- <li>The scope of a <a href="#Predeclared_identifiers">predeclared identifier</a> is the universe block.</li>
-
- <li>The scope of an identifier denoting a constant, type, variable,
- or function (but not method) declared at top level (outside any
- function) is the package block.</li>
-
- <li>The scope of the package name of an imported package is the file block
- of the file containing the import declaration.</li>
-
- <li>The scope of an identifier denoting a method receiver, function parameter,
- or result variable is the function body.</li>
-
- <li>The scope of an identifier denoting a type parameter of a function
- or declared by a method receiver is the function body and all parameter lists of the
- function.
- </li>
-
- <li>The scope of an identifier denoting a type parameter of a type
- begins after the name of the type and ends at the end
- of the TypeSpec.</li>
-
- <li>The scope of a constant or variable identifier declared
- inside a function begins at the end of the ConstSpec or VarSpec
- (ShortVarDecl for short variable declarations)
- and ends at the end of the innermost containing block.</li>
-
- <li>The scope of a type identifier declared inside a function
- begins at the identifier in the TypeSpec
- and ends at the end of the innermost containing block.</li>
-</ol>
-
-<p>
-An identifier declared in a block may be redeclared in an inner block.
-While the identifier of the inner declaration is in scope, it denotes
-the entity declared by the inner declaration.
-</p>
-
-<p>
-The <a href="#Package_clause">package clause</a> is not a declaration; the package name
-does not appear in any scope. Its purpose is to identify the files belonging
-to the same <a href="#Packages">package</a> and to specify the default package name for import
-declarations.
-</p>
-
-
-<h3 id="Label_scopes">Label scopes</h3>
-
-<p>
-Labels are declared by <a href="#Labeled_statements">labeled statements</a> and are
-used in the <a href="#Break_statements">"break"</a>,
-<a href="#Continue_statements">"continue"</a>, and
-<a href="#Goto_statements">"goto"</a> statements.
-It is illegal to define a label that is never used.
-In contrast to other identifiers, labels are not block scoped and do
-not conflict with identifiers that are not labels. The scope of a label
-is the body of the function in which it is declared and excludes
-the body of any nested function.
-</p>
-
-
-<h3 id="Blank_identifier">Blank identifier</h3>
-
-<p>
-The <i>blank identifier</i> is represented by the underscore character <code>_</code>.
-It serves as an anonymous placeholder instead of a regular (non-blank)
-identifier and has special meaning in <a href="#Declarations_and_scope">declarations</a>,
-as an <a href="#Operands">operand</a>, and in <a href="#Assignments">assignments</a>.
-</p>
-
-
-<h3 id="Predeclared_identifiers">Predeclared identifiers</h3>
-
-<p>
-The following identifiers are implicitly declared in the
-<a href="#Blocks">universe block</a>:
-</p>
-<pre class="grammar">
-Types:
- any bool byte comparable
- complex64 complex128 error float32 float64
- int int8 int16 int32 int64 rune string
- uint uint8 uint16 uint32 uint64 uintptr
-
-Constants:
- true false iota
-
-Zero value:
- nil
-
-Functions:
- append cap close complex copy delete imag len
- make new panic print println real recover
-</pre>
-
-<h3 id="Exported_identifiers">Exported identifiers</h3>
-
-<p>
-An identifier may be <i>exported</i> to permit access to it from another package.
-An identifier is exported if both:
-</p>
-<ol>
- <li>the first character of the identifier's name is a Unicode upper case
- letter (Unicode class "Lu"); and</li>
- <li>the identifier is declared in the <a href="#Blocks">package block</a>
- or it is a <a href="#Struct_types">field name</a> or
- <a href="#MethodName">method name</a>.</li>
-</ol>
-<p>
-All other identifiers are not exported.
-</p>
-
-<h3 id="Uniqueness_of_identifiers">Uniqueness of identifiers</h3>
-
-<p>
-Given a set of identifiers, an identifier is called <i>unique</i> if it is
-<i>different</i> from every other in the set.
-Two identifiers are different if they are spelled differently, or if they
-appear in different <a href="#Packages">packages</a> and are not
-<a href="#Exported_identifiers">exported</a>. Otherwise, they are the same.
-</p>
-
-<h3 id="Constant_declarations">Constant declarations</h3>
-
-<p>
-A constant declaration binds a list of identifiers (the names of
-the constants) to the values of a list of <a href="#Constant_expressions">constant expressions</a>.
-The number of identifiers must be equal
-to the number of expressions, and the <i>n</i>th identifier on
-the left is bound to the value of the <i>n</i>th expression on the
-right.
-</p>
-
-<pre class="ebnf">
-ConstDecl = "const" ( ConstSpec | "(" { ConstSpec ";" } ")" ) .
-ConstSpec = IdentifierList [ [ Type ] "=" ExpressionList ] .
-
-IdentifierList = identifier { "," identifier } .
-ExpressionList = Expression { "," Expression } .
-</pre>
-
-<p>
-If the type is present, all constants take the type specified, and
-the expressions must be <a href="#Assignability">assignable</a> to that type,
-which must not be a type parameter.
-If the type is omitted, the constants take the
-individual types of the corresponding expressions.
-If the expression values are untyped <a href="#Constants">constants</a>,
-the declared constants remain untyped and the constant identifiers
-denote the constant values. For instance, if the expression is a
-floating-point literal, the constant identifier denotes a floating-point
-constant, even if the literal's fractional part is zero.
-</p>
-
-<pre>
-const Pi float64 = 3.14159265358979323846
-const zero = 0.0 // untyped floating-point constant
-const (
- size int64 = 1024
- eof = -1 // untyped integer constant
-)
-const a, b, c = 3, 4, "foo" // a = 3, b = 4, c = "foo", untyped integer and string constants
-const u, v float32 = 0, 3 // u = 0.0, v = 3.0
-</pre>
-
-<p>
-Within a parenthesized <code>const</code> declaration list the
-expression list may be omitted from any but the first ConstSpec.
-Such an empty list is equivalent to the textual substitution of the
-first preceding non-empty expression list and its type if any.
-Omitting the list of expressions is therefore equivalent to
-repeating the previous list. The number of identifiers must be equal
-to the number of expressions in the previous list.
-Together with the <a href="#Iota"><code>iota</code> constant generator</a>
-this mechanism permits light-weight declaration of sequential values:
-</p>
-
-<pre>
-const (
- Sunday = iota
- Monday
- Tuesday
- Wednesday
- Thursday
- Friday
- Partyday
- numberOfDays // this constant is not exported
-)
-</pre>
-
-
-<h3 id="Iota">Iota</h3>
-
-<p>
-Within a <a href="#Constant_declarations">constant declaration</a>, the predeclared identifier
-<code>iota</code> represents successive untyped integer <a href="#Constants">
-constants</a>. Its value is the index of the respective <a href="#ConstSpec">ConstSpec</a>
-in that constant declaration, starting at zero.
-It can be used to construct a set of related constants:
-</p>
-
-<pre>
-const (
- c0 = iota // c0 == 0
- c1 = iota // c1 == 1
- c2 = iota // c2 == 2
-)
-
-const (
- a = 1 << iota // a == 1 (iota == 0)
- b = 1 << iota // b == 2 (iota == 1)
- c = 3 // c == 3 (iota == 2, unused)
- d = 1 << iota // d == 8 (iota == 3)
-)
-
-const (
- u = iota * 42 // u == 0 (untyped integer constant)
- v float64 = iota * 42 // v == 42.0 (float64 constant)
- w = iota * 42 // w == 84 (untyped integer constant)
-)
-
-const x = iota // x == 0
-const y = iota // y == 0
-</pre>
-
-<p>
-By definition, multiple uses of <code>iota</code> in the same ConstSpec all have the same value:
-</p>
-
-<pre>
-const (
- bit0, mask0 = 1 << iota, 1<<iota - 1 // bit0 == 1, mask0 == 0 (iota == 0)
- bit1, mask1 // bit1 == 2, mask1 == 1 (iota == 1)
- _, _ // (iota == 2, unused)
- bit3, mask3 // bit3 == 8, mask3 == 7 (iota == 3)
-)
-</pre>
-
-<p>
-This last example exploits the <a href="#Constant_declarations">implicit repetition</a>
-of the last non-empty expression list.
-</p>
-
-
-<h3 id="Type_declarations">Type declarations</h3>
-
-<p>
-A type declaration binds an identifier, the <i>type name</i>, to a <a href="#Types">type</a>.
-Type declarations come in two forms: alias declarations and type definitions.
-</p>
-
-<pre class="ebnf">
-TypeDecl = "type" ( TypeSpec | "(" { TypeSpec ";" } ")" ) .
-TypeSpec = AliasDecl | TypeDef .
-</pre>
-
-<h4 id="Alias_declarations">Alias declarations</h4>
-
-<p>
-An alias declaration binds an identifier to the given type.
-</p>
-
-<pre class="ebnf">
-AliasDecl = identifier "=" Type .
-</pre>
-
-<p>
-Within the <a href="#Declarations_and_scope">scope</a> of
-the identifier, it serves as an <i>alias</i> for the type.
-</p>
-
-<pre>
-type (
- nodeList = []*Node // nodeList and []*Node are identical types
- Polar = polar // Polar and polar denote identical types
-)
-</pre>
-
-
-<h4 id="Type_definitions">Type definitions</h4>
-
-<p>
-A type definition creates a new, distinct type with the same
-<a href="#Types">underlying type</a> and operations as the given type
-and binds an identifier, the <i>type name</i>, to it.
-</p>
-
-<pre class="ebnf">
-TypeDef = identifier [ TypeParameters ] Type .
-</pre>
-
-<p>
-The new type is called a <i>defined type</i>.
-It is <a href="#Type_identity">different</a> from any other type,
-including the type it is created from.
-</p>
-
-<pre>
-type (
- Point struct{ x, y float64 } // Point and struct{ x, y float64 } are different types
- polar Point // polar and Point denote different types
-)
-
-type TreeNode struct {
- left, right *TreeNode
- value any
-}
-
-type Block interface {
- BlockSize() int
- Encrypt(src, dst []byte)
- Decrypt(src, dst []byte)
-}
-</pre>
-
-<p>
-A defined type may have <a href="#Method_declarations">methods</a> associated with it.
-It does not inherit any methods bound to the given type,
-but the <a href="#Method_sets">method set</a>
-of an interface type or of elements of a composite type remains unchanged:
-</p>
-
-<pre>
-// A Mutex is a data type with two methods, Lock and Unlock.
-type Mutex struct { /* Mutex fields */ }
-func (m *Mutex) Lock() { /* Lock implementation */ }
-func (m *Mutex) Unlock() { /* Unlock implementation */ }
-
-// NewMutex has the same composition as Mutex but its method set is empty.
-type NewMutex Mutex
-
-// The method set of PtrMutex's underlying type *Mutex remains unchanged,
-// but the method set of PtrMutex is empty.
-type PtrMutex *Mutex
-
-// The method set of *PrintableMutex contains the methods
-// Lock and Unlock bound to its embedded field Mutex.
-type PrintableMutex struct {
- Mutex
-}
-
-// MyBlock is an interface type that has the same method set as Block.
-type MyBlock Block
-</pre>
-
-<p>
-Type definitions may be used to define different boolean, numeric,
-or string types and associate methods with them:
-</p>
-
-<pre>
-type TimeZone int
-
-const (
- EST TimeZone = -(5 + iota)
- CST
- MST
- PST
-)
-
-func (tz TimeZone) String() string {
- return fmt.Sprintf("GMT%+dh", tz)
-}
-</pre>
-
-<p>
-If the type definition specifies <a href="#Type_parameter_declarations">type parameters</a>,
-the type name denotes a <i>generic type</i>.
-Generic types must be <a href="#Instantiations">instantiated</a> when they
-are used.
-</p>
-
-<pre>
-type List[T any] struct {
- next *List[T]
- value T
-}
-</pre>
-
-<p>
-In a type definition the given type cannot be a type parameter.
-</p>
-
-<pre>
-type T[P any] P // illegal: P is a type parameter
-
-func f[T any]() {
- type L T // illegal: T is a type parameter declared by the enclosing function
-}
-</pre>
-
-<p>
-A generic type may also have <a href="#Method_declarations">methods</a> associated with it.
-In this case, the method receivers must declare the same number of type parameters as
-present in the generic type definition.
-</p>
-
-<pre>
-// The method Len returns the number of elements in the linked list l.
-func (l *List[T]) Len() int { … }
-</pre>
-
-<h3 id="Type_parameter_declarations">Type parameter declarations</h3>
-
-<p>
-A type parameter list declares the <i>type parameters</i> of a generic function or type declaration.
-The type parameter list looks like an ordinary <a href="#Function_types">function parameter list</a>
-except that the type parameter names must all be present and the list is enclosed
-in square brackets rather than parentheses.
-</p>
-
-<pre class="ebnf">
-TypeParameters = "[" TypeParamList [ "," ] "]" .
-TypeParamList = TypeParamDecl { "," TypeParamDecl } .
-TypeParamDecl = IdentifierList TypeConstraint .
-</pre>
-
-<p>
-All non-blank names in the list must be unique.
-Each name declares a type parameter, which is a new and different <a href="#Types">named type</a>
-that acts as a place holder for an (as of yet) unknown type in the declaration.
-The type parameter is replaced with a <i>type argument</i> upon
-<a href="#Instantiations">instantiation</a> of the generic function or type.
-</p>
-
-<pre>
-[P any]
-[S interface{ ~[]byte|string }]
-[S ~[]E, E any]
-[P Constraint[int]]
-[_ any]
-</pre>
-
-<p>
-Just as each ordinary function parameter has a parameter type, each type parameter
-has a corresponding (meta-)type which is called its
-<a href="#Type_constraints"><i>type constraint</i></a>.
-</p>
-
-<p>
-A parsing ambiguity arises when the type parameter list for a generic type
-declares a single type parameter <code>P</code> with a constraint <code>C</code>
-such that the text <code>P C</code> forms a valid expression:
-</p>
-
-<pre>
-type T[P *C] …
-type T[P (C)] …
-type T[P *C|Q] …
-…
-</pre>
-
-<p>
-In these rare cases, the type parameter list is indistinguishable from an
-expression and the type declaration is parsed as an array type declaration.
-To resolve the ambiguity, embed the constraint in an
-<a href="#Interface_types">interface</a> or use a trailing comma:
-</p>
-
-<pre>
-type T[P interface{*C}] …
-type T[P *C,] …
-</pre>
-
-<p>
-Type parameters may also be declared by the receiver specification
-of a <a href="#Method_declarations">method declaration</a> associated
-with a generic type.
-</p>
-
-<!--
-This section needs to explain if and what kind of cycles are permitted
-using type parameters in a type parameter list.
--->
-
-<h4 id="Type_constraints">Type constraints</h4>
-
-<p>
-A type constraint is an <a href="#Interface_types">interface</a> that defines the
-set of permissible type arguments for the respective type parameter and controls the
-operations supported by values of that type parameter.
-</p>
-
-<pre class="ebnf">
-TypeConstraint = TypeElem .
-</pre>
-
-<p>
-If the constraint is an interface literal of the form <code>interface{E}</code> where
-<code>E</code> is an embedded type element (not a method), in a type parameter list
-the enclosing <code>interface{ … }</code> may be omitted for convenience:
-</p>
-
-<pre>
-[T []P] // = [T interface{[]P}]
-[T ~int] // = [T interface{~int}]
-[T int|string] // = [T interface{int|string}]
-type Constraint ~int // illegal: ~int is not inside a type parameter list
-</pre>
-
-<!--
-We should be able to simplify the rules for comparable or delegate some of them
-elsewhere since we have a section that clearly defines how interfaces implement
-other interfaces based on their type sets. But this should get us going for now.
--->
-
-<p>
-The <a href="#Predeclared_identifiers">predeclared</a>
-<a href="#Interface_types">interface type</a> <code>comparable</code>
-denotes the set of all non-interface types that are
-<a href="#Comparison_operators">comparable</a>. Specifically,
-a type <code>T</code> implements <code>comparable</code> if:
-</p>
-
-<ul>
-<li>
- <code>T</code> is not an interface type and <code>T</code> supports the operations
- <code>==</code> and <code>!=</code>; or
-</li>
-<li>
- <code>T</code> is an interface type and each type in <code>T</code>'s
- <a href="#Interface_types">type set</a> implements <code>comparable</code>.
-</li>
-</ul>
-
-<p>
-Even though interfaces that are not type parameters can be
-<a href="#Comparison_operators">compared</a>
-(possibly causing a run-time panic) they do not implement
-<code>comparable</code>.
-</p>
-
-<pre>
-int // implements comparable
-[]byte // does not implement comparable (slices cannot be compared)
-interface{} // does not implement comparable (see above)
-interface{ ~int | ~string } // type parameter only: implements comparable
-interface{ comparable } // type parameter only: implements comparable
-interface{ ~int | ~[]byte } // type parameter only: does not implement comparable (not all types in the type set are comparable)
-</pre>
-
-<p>
-The <code>comparable</code> interface and interfaces that (directly or indirectly) embed
-<code>comparable</code> may only be used as type constraints. They cannot be the types of
-values or variables, or components of other, non-interface types.
-</p>
-
-<h3 id="Variable_declarations">Variable declarations</h3>
-
-<p>
-A variable declaration creates one or more <a href="#Variables">variables</a>,
-binds corresponding identifiers to them, and gives each a type and an initial value.
-</p>
-
-<pre class="ebnf">
-VarDecl = "var" ( VarSpec | "(" { VarSpec ";" } ")" ) .
-VarSpec = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList ) .
-</pre>
-
-<pre>
-var i int
-var U, V, W float64
-var k = 0
-var x, y float32 = -1, -2
-var (
- i int
- u, v, s = 2.0, 3.0, "bar"
-)
-var re, im = complexSqrt(-1)
-var _, found = entries[name] // map lookup; only interested in "found"
-</pre>
-
-<p>
-If a list of expressions is given, the variables are initialized
-with the expressions following the rules for <a href="#Assignments">assignments</a>.
-Otherwise, each variable is initialized to its <a href="#The_zero_value">zero value</a>.
-</p>
-
-<p>
-If a type is present, each variable is given that type.
-Otherwise, each variable is given the type of the corresponding
-initialization value in the assignment.
-If that value is an untyped constant, it is first implicitly
-<a href="#Conversions">converted</a> to its <a href="#Constants">default type</a>;
-if it is an untyped boolean value, it is first implicitly converted to type <code>bool</code>.
-The predeclared value <code>nil</code> cannot be used to initialize a variable
-with no explicit type.
-</p>
-
-<pre>
-var d = math.Sin(0.5) // d is float64
-var i = 42 // i is int
-var t, ok = x.(T) // t is T, ok is bool
-var n = nil // illegal
-</pre>
-
-<p>
-Implementation restriction: A compiler may make it illegal to declare a variable
-inside a <a href="#Function_declarations">function body</a> if the variable is
-never used.
-</p>
-
-<h3 id="Short_variable_declarations">Short variable declarations</h3>
-
-<p>
-A <i>short variable declaration</i> uses the syntax:
-</p>
-
-<pre class="ebnf">
-ShortVarDecl = IdentifierList ":=" ExpressionList .
-</pre>
-
-<p>
-It is shorthand for a regular <a href="#Variable_declarations">variable declaration</a>
-with initializer expressions but no types:
-</p>
-
-<pre class="grammar">
-"var" IdentifierList = ExpressionList .
-</pre>
-
-<pre>
-i, j := 0, 10
-f := func() int { return 7 }
-ch := make(chan int)
-r, w, _ := os.Pipe() // os.Pipe() returns a connected pair of Files and an error, if any
-_, y, _ := coord(p) // coord() returns three values; only interested in y coordinate
-</pre>
-
-<p>
-Unlike regular variable declarations, a short variable declaration may <i>redeclare</i>
-variables provided they were originally declared earlier in the same block
-(or the parameter lists if the block is the function body) with the same type,
-and at least one of the non-<a href="#Blank_identifier">blank</a> variables is new.
-As a consequence, redeclaration can only appear in a multi-variable short declaration.
-Redeclaration does not introduce a new variable; it just assigns a new value to the original.
-</p>
-
-<pre>
-field1, offset := nextField(str, 0)
-field2, offset := nextField(str, offset) // redeclares offset
-a, a := 1, 2 // illegal: double declaration of a or no new variable if a was declared elsewhere
-</pre>
-
-<p>
-Short variable declarations may appear only inside functions.
-In some contexts such as the initializers for
-<a href="#If_statements">"if"</a>,
-<a href="#For_statements">"for"</a>, or
-<a href="#Switch_statements">"switch"</a> statements,
-they can be used to declare local temporary variables.
-</p>
-
-<h3 id="Function_declarations">Function declarations</h3>
-
-<!--
- Given the importance of functions, this section has always
- been woefully underdeveloped. Would be nice to expand this
- a bit.
--->
-
-<p>
-A function declaration binds an identifier, the <i>function name</i>,
-to a function.
-</p>
-
-<pre class="ebnf">
-FunctionDecl = "func" FunctionName [ TypeParameters ] Signature [ FunctionBody ] .
-FunctionName = identifier .
-FunctionBody = Block .
-</pre>
-
-<p>
-If the function's <a href="#Function_types">signature</a> declares
-result parameters, the function body's statement list must end in
-a <a href="#Terminating_statements">terminating statement</a>.
-</p>
-
-<pre>
-func IndexRune(s string, r rune) int {
- for i, c := range s {
- if c == r {
- return i
- }
- }
- // invalid: missing return statement
-}
-</pre>
-
-<p>
-If the function declaration specifies <a href="#Type_parameter_declarations">type parameters</a>,
-the function name denotes a <i>generic function</i>.
-A generic function must be <a href="#Instantiations">instantiated</a> before it can be
-called or used as a value.
-</p>
-
-<pre>
-func min[T ~int|~float64](x, y T) T {
- if x < y {
- return x
- }
- return y
-}
-</pre>
-
-<p>
-A function declaration without type parameters may omit the body.
-Such a declaration provides the signature for a function implemented outside Go,
-such as an assembly routine.
-</p>
-
-<pre>
-func flushICache(begin, end uintptr) // implemented externally
-</pre>
-
-<h3 id="Method_declarations">Method declarations</h3>
-
-<p>
-A method is a <a href="#Function_declarations">function</a> with a <i>receiver</i>.
-A method declaration binds an identifier, the <i>method name</i>, to a method,
-and associates the method with the receiver's <i>base type</i>.
-</p>
-
-<pre class="ebnf">
-MethodDecl = "func" Receiver MethodName Signature [ FunctionBody ] .
-Receiver = Parameters .
-</pre>
-
-<p>
-The receiver is specified via an extra parameter section preceding the method
-name. That parameter section must declare a single non-variadic parameter, the receiver.
-Its type must be a <a href="#Type_definitions">defined</a> type <code>T</code> or a
-pointer to a defined type <code>T</code>, possibly followed by a list of type parameter
-names <code>[P1, P2, …]</code> enclosed in square brackets.
-<code>T</code> is called the receiver <i>base type</i>. A receiver base type cannot be
-a pointer or interface type and it must be defined in the same package as the method.
-The method is said to be <i>bound</i> to its receiver base type and the method name
-is visible only within <a href="#Selectors">selectors</a> for type <code>T</code>
-or <code>*T</code>.
-</p>
-
-<p>
-A non-<a href="#Blank_identifier">blank</a> receiver identifier must be
-<a href="#Uniqueness_of_identifiers">unique</a> in the method signature.
-If the receiver's value is not referenced inside the body of the method,
-its identifier may be omitted in the declaration. The same applies in
-general to parameters of functions and methods.
-</p>
-
-<p>
-For a base type, the non-blank names of methods bound to it must be unique.
-If the base type is a <a href="#Struct_types">struct type</a>,
-the non-blank method and field names must be distinct.
-</p>
-
-<p>
-Given defined type <code>Point</code> the declarations
-</p>
-
-<pre>
-func (p *Point) Length() float64 {
- return math.Sqrt(p.x * p.x + p.y * p.y)
-}
-
-func (p *Point) Scale(factor float64) {
- p.x *= factor
- p.y *= factor
-}
-</pre>
-
-<p>
-bind the methods <code>Length</code> and <code>Scale</code>,
-with receiver type <code>*Point</code>,
-to the base type <code>Point</code>.
-</p>
-
-<p>
-If the receiver base type is a <a href="#Type_declarations">generic type</a>, the
-receiver specification must declare corresponding type parameters for the method
-to use. This makes the receiver type parameters available to the method.
-Syntactically, this type parameter declaration looks like an
-<a href="#Instantiations">instantiation</a> of the receiver base type: the type
-arguments must be identifiers denoting the type parameters being declared, one
-for each type parameter of the receiver base type.
-The type parameter names do not need to match their corresponding parameter names in the
-receiver base type definition, and all non-blank parameter names must be unique in the
-receiver parameter section and the method signature.
-The receiver type parameter constraints are implied by the receiver base type definition:
-corresponding type parameters have corresponding constraints.
-</p>
-
-<pre>
-type Pair[A, B any] struct {
- a A
- b B
-}
-
-func (p Pair[A, B]) Swap() Pair[B, A] { … } // receiver declares A, B
-func (p Pair[First, _]) First() First { … } // receiver declares First, corresponds to A in Pair
-</pre>
-
-<h2 id="Expressions">Expressions</h2>
-
-<p>
-An expression specifies the computation of a value by applying
-operators and functions to operands.
-</p>
-
-<h3 id="Operands">Operands</h3>
-
-<p>
-Operands denote the elementary values in an expression. An operand may be a
-literal, a (possibly <a href="#Qualified_identifiers">qualified</a>)
-non-<a href="#Blank_identifier">blank</a> identifier denoting a
-<a href="#Constant_declarations">constant</a>,
-<a href="#Variable_declarations">variable</a>, or
-<a href="#Function_declarations">function</a>,
-or a parenthesized expression.
-</p>
-
-<pre class="ebnf">
-Operand = Literal | OperandName [ TypeArgs ] | "(" Expression ")" .
-Literal = BasicLit | CompositeLit | FunctionLit .
-BasicLit = int_lit | float_lit | imaginary_lit | rune_lit | string_lit .
-OperandName = identifier | QualifiedIdent .
-</pre>
-
-<p>
-An operand name denoting a <a href="#Function_declarations">generic function</a>
-may be followed by a list of <a href="#Instantiations">type arguments</a>; the
-resulting operand is an <a href="#Instantiations">instantiated</a> function.
-</p>
-
-<p>
-The <a href="#Blank_identifier">blank identifier</a> may appear as an
-operand only on the left-hand side of an <a href="#Assignments">assignment</a>.
-</p>
-
-<p>
-Implementation restriction: A compiler need not report an error if an operand's
-type is a <a href="#Type_parameter_declarations">type parameter</a> with an empty
-<a href="#Interface_types">type set</a>. Functions with such type parameters
-cannot be <a href="#Instantiations">instantiated</a>; any attempt will lead
-to an error at the instantiation site.
-</p>
-
-<h3 id="Qualified_identifiers">Qualified identifiers</h3>
-
-<p>
-A <i>qualified identifier</i> is an identifier qualified with a package name prefix.
-Both the package name and the identifier must not be
-<a href="#Blank_identifier">blank</a>.
-</p>
-
-<pre class="ebnf">
-QualifiedIdent = PackageName "." identifier .
-</pre>
-
-<p>
-A qualified identifier accesses an identifier in a different package, which
-must be <a href="#Import_declarations">imported</a>.
-The identifier must be <a href="#Exported_identifiers">exported</a> and
-declared in the <a href="#Blocks">package block</a> of that package.
-</p>
-
-<pre>
-math.Sin // denotes the Sin function in package math
-</pre>
-
-<h3 id="Composite_literals">Composite literals</h3>
-
-<p>
-Composite literals construct new composite values each time they are evaluated.
-They consist of the type of the literal followed by a brace-bound list of elements.
-Each element may optionally be preceded by a corresponding key.
-</p>
-
-<pre class="ebnf">
-CompositeLit = LiteralType LiteralValue .
-LiteralType = StructType | ArrayType | "[" "..." "]" ElementType |
- SliceType | MapType | TypeName .
-LiteralValue = "{" [ ElementList [ "," ] ] "}" .
-ElementList = KeyedElement { "," KeyedElement } .
-KeyedElement = [ Key ":" ] Element .
-Key = FieldName | Expression | LiteralValue .
-FieldName = identifier .
-Element = Expression | LiteralValue .
-</pre>
-
-<p>
-The LiteralType's <a href="#Core_types">core type</a> <code>T</code>
-must be a struct, array, slice, or map type
-(the grammar enforces this constraint except when the type is given
-as a TypeName).
-The types of the elements and keys must be <a href="#Assignability">assignable</a>
-to the respective field, element, and key types of type <code>T</code>;
-there is no additional conversion.
-The key is interpreted as a field name for struct literals,
-an index for array and slice literals, and a key for map literals.
-For map literals, all elements must have a key. It is an error
-to specify multiple elements with the same field name or
-constant key value. For non-constant map keys, see the section on
-<a href="#Order_of_evaluation">evaluation order</a>.
-</p>
-
-<p>
-For struct literals the following rules apply:
-</p>
-<ul>
- <li>A key must be a field name declared in the struct type.
- </li>
- <li>An element list that does not contain any keys must
- list an element for each struct field in the
- order in which the fields are declared.
- </li>
- <li>If any element has a key, every element must have a key.
- </li>
- <li>An element list that contains keys does not need to
- have an element for each struct field. Omitted fields
- get the zero value for that field.
- </li>
- <li>A literal may omit the element list; such a literal evaluates
- to the zero value for its type.
- </li>
- <li>It is an error to specify an element for a non-exported
- field of a struct belonging to a different package.
- </li>
-</ul>
-
-<p>
-Given the declarations
-</p>
-<pre>
-type Point3D struct { x, y, z float64 }
-type Line struct { p, q Point3D }
-</pre>
-
-<p>
-one may write
-</p>
-
-<pre>
-origin := Point3D{} // zero value for Point3D
-line := Line{origin, Point3D{y: -4, z: 12.3}} // zero value for line.q.x
-</pre>
-
-<p>
-For array and slice literals the following rules apply:
-</p>
-<ul>
- <li>Each element has an associated integer index marking
- its position in the array.
- </li>
- <li>An element with a key uses the key as its index. The
- key must be a non-negative constant
- <a href="#Representability">representable</a> by
- a value of type <code>int</code>; and if it is typed
- it must be of <a href="#Numeric_types">integer type</a>.
- </li>
- <li>An element without a key uses the previous element's index plus one.
- If the first element has no key, its index is zero.
- </li>
-</ul>
-
-<p>
-<a href="#Address_operators">Taking the address</a> of a composite literal
-generates a pointer to a unique <a href="#Variables">variable</a> initialized
-with the literal's value.
-</p>
-
-<pre>
-var pointer *Point3D = &Point3D{y: 1000}
-</pre>
-
-<p>
-Note that the <a href="#The_zero_value">zero value</a> for a slice or map
-type is not the same as an initialized but empty value of the same type.
-Consequently, taking the address of an empty slice or map composite literal
-does not have the same effect as allocating a new slice or map value with
-<a href="#Allocation">new</a>.
-</p>
-
-<pre>
-p1 := &[]int{} // p1 points to an initialized, empty slice with value []int{} and length 0
-p2 := new([]int) // p2 points to an uninitialized slice with value nil and length 0
-</pre>
-
-<p>
-The length of an array literal is the length specified in the literal type.
-If fewer elements than the length are provided in the literal, the missing
-elements are set to the zero value for the array element type.
-It is an error to provide elements with index values outside the index range
-of the array. The notation <code>...</code> specifies an array length equal
-to the maximum element index plus one.
-</p>
-
-<pre>
-buffer := [10]string{} // len(buffer) == 10
-intSet := [6]int{1, 2, 3, 5} // len(intSet) == 6
-days := [...]string{"Sat", "Sun"} // len(days) == 2
-</pre>
-
-<p>
-A slice literal describes the entire underlying array literal.
-Thus the length and capacity of a slice literal are the maximum
-element index plus one. A slice literal has the form
-</p>
-
-<pre>
-[]T{x1, x2, … xn}
-</pre>
-
-<p>
-and is shorthand for a slice operation applied to an array:
-</p>
-
-<pre>
-tmp := [n]T{x1, x2, … xn}
-tmp[0 : n]
-</pre>
-
-<p>
-Within a composite literal of array, slice, or map type <code>T</code>,
-elements or map keys that are themselves composite literals may elide the respective
-literal type if it is identical to the element or key type of <code>T</code>.
-Similarly, elements or keys that are addresses of composite literals may elide
-the <code>&T</code> when the element or key type is <code>*T</code>.
-</p>
-
-<pre>
-[...]Point{{1.5, -3.5}, {0, 0}} // same as [...]Point{Point{1.5, -3.5}, Point{0, 0}}
-[][]int{{1, 2, 3}, {4, 5}} // same as [][]int{[]int{1, 2, 3}, []int{4, 5}}
-[][]Point{{{0, 1}, {1, 2}}} // same as [][]Point{[]Point{Point{0, 1}, Point{1, 2}}}
-map[string]Point{"orig": {0, 0}} // same as map[string]Point{"orig": Point{0, 0}}
-map[Point]string{{0, 0}: "orig"} // same as map[Point]string{Point{0, 0}: "orig"}
-
-type PPoint *Point
-[2]*Point{{1.5, -3.5}, {}} // same as [2]*Point{&Point{1.5, -3.5}, &Point{}}
-[2]PPoint{{1.5, -3.5}, {}} // same as [2]PPoint{PPoint(&Point{1.5, -3.5}), PPoint(&Point{})}
-</pre>
-
-<p>
-A parsing ambiguity arises when a composite literal using the
-TypeName form of the LiteralType appears as an operand between the
-<a href="#Keywords">keyword</a> and the opening brace of the block
-of an "if", "for", or "switch" statement, and the composite literal
-is not enclosed in parentheses, square brackets, or curly braces.
-In this rare case, the opening brace of the literal is erroneously parsed
-as the one introducing the block of statements. To resolve the ambiguity,
-the composite literal must appear within parentheses.
-</p>
-
-<pre>
-if x == (T{a,b,c}[i]) { … }
-if (x == T{a,b,c}[i]) { … }
-</pre>
-
-<p>
-Examples of valid array, slice, and map literals:
-</p>
-
-<pre>
-// list of prime numbers
-primes := []int{2, 3, 5, 7, 9, 2147483647}
-
-// vowels[ch] is true if ch is a vowel
-vowels := [128]bool{'a': true, 'e': true, 'i': true, 'o': true, 'u': true, 'y': true}
-
-// the array [10]float32{-1, 0, 0, 0, -0.1, -0.1, 0, 0, 0, -1}
-filter := [10]float32{-1, 4: -0.1, -0.1, 9: -1}
-
-// frequencies in Hz for equal-tempered scale (A4 = 440Hz)
-noteFrequency := map[string]float32{
- "C0": 16.35, "D0": 18.35, "E0": 20.60, "F0": 21.83,
- "G0": 24.50, "A0": 27.50, "B0": 30.87,
-}
-</pre>
-
-
-<h3 id="Function_literals">Function literals</h3>
-
-<p>
-A function literal represents an anonymous <a href="#Function_declarations">function</a>.
-Function literals cannot declare type parameters.
-</p>
-
-<pre class="ebnf">
-FunctionLit = "func" Signature FunctionBody .
-</pre>
-
-<pre>
-func(a, b int, z float64) bool { return a*b < int(z) }
-</pre>
-
-<p>
-A function literal can be assigned to a variable or invoked directly.
-</p>
-
-<pre>
-f := func(x, y int) int { return x + y }
-func(ch chan int) { ch <- ACK }(replyChan)
-</pre>
-
-<p>
-Function literals are <i>closures</i>: they may refer to variables
-defined in a surrounding function. Those variables are then shared between
-the surrounding function and the function literal, and they survive as long
-as they are accessible.
-</p>
-
-
-<h3 id="Primary_expressions">Primary expressions</h3>
-
-<p>
-Primary expressions are the operands for unary and binary expressions.
-</p>
-
-<pre class="ebnf">
-PrimaryExpr =
- Operand |
- Conversion |
- MethodExpr |
- PrimaryExpr Selector |
- PrimaryExpr Index |
- PrimaryExpr Slice |
- PrimaryExpr TypeAssertion |
- PrimaryExpr Arguments .
-
-Selector = "." identifier .
-Index = "[" Expression "]" .
-Slice = "[" [ Expression ] ":" [ Expression ] "]" |
- "[" [ Expression ] ":" Expression ":" Expression "]" .
-TypeAssertion = "." "(" Type ")" .
-Arguments = "(" [ ( ExpressionList | Type [ "," ExpressionList ] ) [ "..." ] [ "," ] ] ")" .
-</pre>
-
-
-<pre>
-x
-2
-(s + ".txt")
-f(3.1415, true)
-Point{1, 2}
-m["foo"]
-s[i : j + 1]
-obj.color
-f.p[i].x()
-</pre>
-
-
-<h3 id="Selectors">Selectors</h3>
-
-<p>
-For a <a href="#Primary_expressions">primary expression</a> <code>x</code>
-that is not a <a href="#Package_clause">package name</a>, the
-<i>selector expression</i>
-</p>
-
-<pre>
-x.f
-</pre>
-
-<p>
-denotes the field or method <code>f</code> of the value <code>x</code>
-(or sometimes <code>*x</code>; see below).
-The identifier <code>f</code> is called the (field or method) <i>selector</i>;
-it must not be the <a href="#Blank_identifier">blank identifier</a>.
-The type of the selector expression is the type of <code>f</code>.
-If <code>x</code> is a package name, see the section on
-<a href="#Qualified_identifiers">qualified identifiers</a>.
-</p>
-
-<p>
-A selector <code>f</code> may denote a field or method <code>f</code> of
-a type <code>T</code>, or it may refer
-to a field or method <code>f</code> of a nested
-<a href="#Struct_types">embedded field</a> of <code>T</code>.
-The number of embedded fields traversed
-to reach <code>f</code> is called its <i>depth</i> in <code>T</code>.
-The depth of a field or method <code>f</code>
-declared in <code>T</code> is zero.
-The depth of a field or method <code>f</code> declared in
-an embedded field <code>A</code> in <code>T</code> is the
-depth of <code>f</code> in <code>A</code> plus one.
-</p>
-
-<p>
-The following rules apply to selectors:
-</p>
-
-<ol>
-<li>
-For a value <code>x</code> of type <code>T</code> or <code>*T</code>
-where <code>T</code> is not a pointer or interface type,
-<code>x.f</code> denotes the field or method at the shallowest depth
-in <code>T</code> where there is such an <code>f</code>.
-If there is not exactly <a href="#Uniqueness_of_identifiers">one <code>f</code></a>
-with shallowest depth, the selector expression is illegal.
-</li>
-
-<li>
-For a value <code>x</code> of type <code>I</code> where <code>I</code>
-is an interface type, <code>x.f</code> denotes the actual method with name
-<code>f</code> of the dynamic value of <code>x</code>.
-If there is no method with name <code>f</code> in the
-<a href="#Method_sets">method set</a> of <code>I</code>, the selector
-expression is illegal.
-</li>
-
-<li>
-As an exception, if the type of <code>x</code> is a <a href="#Type_definitions">defined</a>
-pointer type and <code>(*x).f</code> is a valid selector expression denoting a field
-(but not a method), <code>x.f</code> is shorthand for <code>(*x).f</code>.
-</li>
-
-<li>
-In all other cases, <code>x.f</code> is illegal.
-</li>
-
-<li>
-If <code>x</code> is of pointer type and has the value
-<code>nil</code> and <code>x.f</code> denotes a struct field,
-assigning to or evaluating <code>x.f</code>
-causes a <a href="#Run_time_panics">run-time panic</a>.
-</li>
-
-<li>
-If <code>x</code> is of interface type and has the value
-<code>nil</code>, <a href="#Calls">calling</a> or
-<a href="#Method_values">evaluating</a> the method <code>x.f</code>
-causes a <a href="#Run_time_panics">run-time panic</a>.
-</li>
-</ol>
-
-<p>
-For example, given the declarations:
-</p>
-
-<pre>
-type T0 struct {
- x int
-}
-
-func (*T0) M0()
-
-type T1 struct {
- y int
-}
-
-func (T1) M1()
-
-type T2 struct {
- z int
- T1
- *T0
-}
-
-func (*T2) M2()
-
-type Q *T2
-
-var t T2 // with t.T0 != nil
-var p *T2 // with p != nil and (*p).T0 != nil
-var q Q = p
-</pre>
-
-<p>
-one may write:
-</p>
-
-<pre>
-t.z // t.z
-t.y // t.T1.y
-t.x // (*t.T0).x
-
-p.z // (*p).z
-p.y // (*p).T1.y
-p.x // (*(*p).T0).x
-
-q.x // (*(*q).T0).x (*q).x is a valid field selector
-
-p.M0() // ((*p).T0).M0() M0 expects *T0 receiver
-p.M1() // ((*p).T1).M1() M1 expects T1 receiver
-p.M2() // p.M2() M2 expects *T2 receiver
-t.M2() // (&t).M2() M2 expects *T2 receiver, see section on Calls
-</pre>
-
-<p>
-but the following is invalid:
-</p>
-
-<pre>
-q.M0() // (*q).M0 is valid but not a field selector
-</pre>
-
-
-<h3 id="Method_expressions">Method expressions</h3>
-
-<p>
-If <code>M</code> is in the <a href="#Method_sets">method set</a> of type <code>T</code>,
-<code>T.M</code> is a function that is callable as a regular function
-with the same arguments as <code>M</code> prefixed by an additional
-argument that is the receiver of the method.
-</p>
-
-<pre class="ebnf">
-MethodExpr = ReceiverType "." MethodName .
-ReceiverType = Type .
-</pre>
-
-<p>
-Consider a struct type <code>T</code> with two methods,
-<code>Mv</code>, whose receiver is of type <code>T</code>, and
-<code>Mp</code>, whose receiver is of type <code>*T</code>.
-</p>
-
-<pre>
-type T struct {
- a int
-}
-func (tv T) Mv(a int) int { return 0 } // value receiver
-func (tp *T) Mp(f float32) float32 { return 1 } // pointer receiver
-
-var t T
-</pre>
-
-<p>
-The expression
-</p>
-
-<pre>
-T.Mv
-</pre>
-
-<p>
-yields a function equivalent to <code>Mv</code> but
-with an explicit receiver as its first argument; it has signature
-</p>
-
-<pre>
-func(tv T, a int) int
-</pre>
-
-<p>
-That function may be called normally with an explicit receiver, so
-these five invocations are equivalent:
-</p>
-
-<pre>
-t.Mv(7)
-T.Mv(t, 7)
-(T).Mv(t, 7)
-f1 := T.Mv; f1(t, 7)
-f2 := (T).Mv; f2(t, 7)
-</pre>
-
-<p>
-Similarly, the expression
-</p>
-
-<pre>
-(*T).Mp
-</pre>
-
-<p>
-yields a function value representing <code>Mp</code> with signature
-</p>
-
-<pre>
-func(tp *T, f float32) float32
-</pre>
-
-<p>
-For a method with a value receiver, one can derive a function
-with an explicit pointer receiver, so
-</p>
-
-<pre>
-(*T).Mv
-</pre>
-
-<p>
-yields a function value representing <code>Mv</code> with signature
-</p>
-
-<pre>
-func(tv *T, a int) int
-</pre>
-
-<p>
-Such a function indirects through the receiver to create a value
-to pass as the receiver to the underlying method;
-the method does not overwrite the value whose address is passed in
-the function call.
-</p>
-
-<p>
-The final case, a value-receiver function for a pointer-receiver method,
-is illegal because pointer-receiver methods are not in the method set
-of the value type.
-</p>
-
-<p>
-Function values derived from methods are called with function call syntax;
-the receiver is provided as the first argument to the call.
-That is, given <code>f := T.Mv</code>, <code>f</code> is invoked
-as <code>f(t, 7)</code> not <code>t.f(7)</code>.
-To construct a function that binds the receiver, use a
-<a href="#Function_literals">function literal</a> or
-<a href="#Method_values">method value</a>.
-</p>
-
-<p>
-It is legal to derive a function value from a method of an interface type.
-The resulting function takes an explicit receiver of that interface type.
-</p>
-
-<h3 id="Method_values">Method values</h3>
-
-<p>
-If the expression <code>x</code> has static type <code>T</code> and
-<code>M</code> is in the <a href="#Method_sets">method set</a> of type <code>T</code>,
-<code>x.M</code> is called a <i>method value</i>.
-The method value <code>x.M</code> is a function value that is callable
-with the same arguments as a method call of <code>x.M</code>.
-The expression <code>x</code> is evaluated and saved during the evaluation of the
-method value; the saved copy is then used as the receiver in any calls,
-which may be executed later.
-</p>
-
-<pre>
-type S struct { *T }
-type T int
-func (t T) M() { print(t) }
-
-t := new(T)
-s := S{T: t}
-f := t.M // receiver *t is evaluated and stored in f
-g := s.M // receiver *(s.T) is evaluated and stored in g
-*t = 42 // does not affect stored receivers in f and g
-</pre>
-
-<p>
-The type <code>T</code> may be an interface or non-interface type.
-</p>
-
-<p>
-As in the discussion of <a href="#Method_expressions">method expressions</a> above,
-consider a struct type <code>T</code> with two methods,
-<code>Mv</code>, whose receiver is of type <code>T</code>, and
-<code>Mp</code>, whose receiver is of type <code>*T</code>.
-</p>
-
-<pre>
-type T struct {
- a int
-}
-func (tv T) Mv(a int) int { return 0 } // value receiver
-func (tp *T) Mp(f float32) float32 { return 1 } // pointer receiver
-
-var t T
-var pt *T
-func makeT() T
-</pre>
-
-<p>
-The expression
-</p>
-
-<pre>
-t.Mv
-</pre>
-
-<p>
-yields a function value of type
-</p>
-
-<pre>
-func(int) int
-</pre>
-
-<p>
-These two invocations are equivalent:
-</p>
-
-<pre>
-t.Mv(7)
-f := t.Mv; f(7)
-</pre>
-
-<p>
-Similarly, the expression
-</p>
-
-<pre>
-pt.Mp
-</pre>
-
-<p>
-yields a function value of type
-</p>
-
-<pre>
-func(float32) float32
-</pre>
-
-<p>
-As with <a href="#Selectors">selectors</a>, a reference to a non-interface method with a value receiver
-using a pointer will automatically dereference that pointer: <code>pt.Mv</code> is equivalent to <code>(*pt).Mv</code>.
-</p>
-
-<p>
-As with <a href="#Calls">method calls</a>, a reference to a non-interface method with a pointer receiver
-using an addressable value will automatically take the address of that value: <code>t.Mp</code> is equivalent to <code>(&t).Mp</code>.
-</p>
-
-<pre>
-f := t.Mv; f(7) // like t.Mv(7)
-f := pt.Mp; f(7) // like pt.Mp(7)
-f := pt.Mv; f(7) // like (*pt).Mv(7)
-f := t.Mp; f(7) // like (&t).Mp(7)
-f := makeT().Mp // invalid: result of makeT() is not addressable
-</pre>
-
-<p>
-Although the examples above use non-interface types, it is also legal to create a method value
-from a value of interface type.
-</p>
-
-<pre>
-var i interface { M(int) } = myVal
-f := i.M; f(7) // like i.M(7)
-</pre>
-
-
-<h3 id="Index_expressions">Index expressions</h3>
-
-<p>
-A primary expression of the form
-</p>
-
-<pre>
-a[x]
-</pre>
-
-<p>
-denotes the element of the array, pointer to array, slice, string or map <code>a</code> indexed by <code>x</code>.
-The value <code>x</code> is called the <i>index</i> or <i>map key</i>, respectively.
-The following rules apply:
-</p>
-
-<p>
-If <code>a</code> is neither a map nor a type parameter:
-</p>
-<ul>
- <li>the index <code>x</code> must be an untyped constant or its
- <a href="#Core_types">core type</a> must be an <a href="#Numeric_types">integer</a></li>
- <li>a constant index must be non-negative and
- <a href="#Representability">representable</a> by a value of type <code>int</code></li>
- <li>a constant index that is untyped is given type <code>int</code></li>
- <li>the index <code>x</code> is <i>in range</i> if <code>0 <= x < len(a)</code>,
- otherwise it is <i>out of range</i></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Array_types">array type</a> <code>A</code>:
-</p>
-<ul>
- <li>a <a href="#Constants">constant</a> index must be in range</li>
- <li>if <code>x</code> is out of range at run time,
- a <a href="#Run_time_panics">run-time panic</a> occurs</li>
- <li><code>a[x]</code> is the array element at index <code>x</code> and the type of
- <code>a[x]</code> is the element type of <code>A</code></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Pointer_types">pointer</a> to array type:
-</p>
-<ul>
- <li><code>a[x]</code> is shorthand for <code>(*a)[x]</code></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Slice_types">slice type</a> <code>S</code>:
-</p>
-<ul>
- <li>if <code>x</code> is out of range at run time,
- a <a href="#Run_time_panics">run-time panic</a> occurs</li>
- <li><code>a[x]</code> is the slice element at index <code>x</code> and the type of
- <code>a[x]</code> is the element type of <code>S</code></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#String_types">string type</a>:
-</p>
-<ul>
- <li>a <a href="#Constants">constant</a> index must be in range
- if the string <code>a</code> is also constant</li>
- <li>if <code>x</code> is out of range at run time,
- a <a href="#Run_time_panics">run-time panic</a> occurs</li>
- <li><code>a[x]</code> is the non-constant byte value at index <code>x</code> and the type of
- <code>a[x]</code> is <code>byte</code></li>
- <li><code>a[x]</code> may not be assigned to</li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Map_types">map type</a> <code>M</code>:
-</p>
-<ul>
- <li><code>x</code>'s type must be
- <a href="#Assignability">assignable</a>
- to the key type of <code>M</code></li>
- <li>if the map contains an entry with key <code>x</code>,
- <code>a[x]</code> is the map element with key <code>x</code>
- and the type of <code>a[x]</code> is the element type of <code>M</code></li>
- <li>if the map is <code>nil</code> or does not contain such an entry,
- <code>a[x]</code> is the <a href="#The_zero_value">zero value</a>
- for the element type of <code>M</code></li>
-</ul>
-
-<p>
-For <code>a</code> of <a href="#Type_parameter_declarations">type parameter type</a> <code>P</code>:
-</p>
-<ul>
- <li>The index expression <code>a[x]</code> must be valid for values
- of all types in <code>P</code>'s type set.</li>
- <li>The element types of all types in <code>P</code>'s type set must be identical.
- In this context, the element type of a string type is <code>byte</code>.</li>
- <li>If there is a map type in the type set of <code>P</code>,
- all types in that type set must be map types, and the respective key types
- must be all identical.</li>
- <li><code>a[x]</code> is the array, slice, or string element at index <code>x</code>,
- or the map element with key <code>x</code> of the type argument
- that <code>P</code> is instantiated with, and the type of <code>a[x]</code> is
- the type of the (identical) element types.</li>
- <li><code>a[x]</code> may not be assigned to if <code>P</code>'s type set
- includes string types.
-</ul>
-
-<p>
-Otherwise <code>a[x]</code> is illegal.
-</p>
-
-<p>
-An index expression on a map <code>a</code> of type <code>map[K]V</code>
-used in an <a href="#Assignments">assignment</a> or initialization of the special form
-</p>
-
-<pre>
-v, ok = a[x]
-v, ok := a[x]
-var v, ok = a[x]
-</pre>
-
-<p>
-yields an additional untyped boolean value. The value of <code>ok</code> is
-<code>true</code> if the key <code>x</code> is present in the map, and
-<code>false</code> otherwise.
-</p>
-
-<p>
-Assigning to an element of a <code>nil</code> map causes a
-<a href="#Run_time_panics">run-time panic</a>.
-</p>
-
-
-<h3 id="Slice_expressions">Slice expressions</h3>
-
-<p>
-Slice expressions construct a substring or slice from a string, array, pointer
-to array, or slice. There are two variants: a simple form that specifies a low
-and high bound, and a full form that also specifies a bound on the capacity.
-</p>
-
-<h4>Simple slice expressions</h4>
-
-<p>
-The primary expression
-</p>
-
-<pre>
-a[low : high]
-</pre>
-
-<p>
-constructs a substring or slice. The <a href="#Core_types">core type</a> of
-<code>a</code> must be a string, array, pointer to array, or slice.
-The <i>indices</i> <code>low</code> and
-<code>high</code> select which elements of operand <code>a</code> appear
-in the result. The result has indices starting at 0 and length equal to
-<code>high</code> - <code>low</code>.
-After slicing the array <code>a</code>
-</p>
-
-<pre>
-a := [5]int{1, 2, 3, 4, 5}
-s := a[1:4]
-</pre>
-
-<p>
-the slice <code>s</code> has type <code>[]int</code>, length 3, capacity 4, and elements
-</p>
-
-<pre>
-s[0] == 2
-s[1] == 3
-s[2] == 4
-</pre>
-
-<p>
-For convenience, any of the indices may be omitted. A missing <code>low</code>
-index defaults to zero; a missing <code>high</code> index defaults to the length of the
-sliced operand:
-</p>
-
-<pre>
-a[2:] // same as a[2 : len(a)]
-a[:3] // same as a[0 : 3]
-a[:] // same as a[0 : len(a)]
-</pre>
-
-<p>
-If <code>a</code> is a pointer to an array, <code>a[low : high]</code> is shorthand for
-<code>(*a)[low : high]</code>.
-</p>
-
-<p>
-For arrays or strings, the indices are <i>in range</i> if
-<code>0</code> <= <code>low</code> <= <code>high</code> <= <code>len(a)</code>,
-otherwise they are <i>out of range</i>.
-For slices, the upper index bound is the slice capacity <code>cap(a)</code> rather than the length.
-A <a href="#Constants">constant</a> index must be non-negative and
-<a href="#Representability">representable</a> by a value of type
-<code>int</code>; for arrays or constant strings, constant indices must also be in range.
-If both indices are constant, they must satisfy <code>low <= high</code>.
-If the indices are out of range at run time, a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<p>
-Except for <a href="#Constants">untyped strings</a>, if the sliced operand is a string or slice,
-the result of the slice operation is a non-constant value of the same type as the operand.
-For untyped string operands the result is a non-constant value of type <code>string</code>.
-If the sliced operand is an array, it must be <a href="#Address_operators">addressable</a>
-and the result of the slice operation is a slice with the same element type as the array.
-</p>
-
-<p>
-If the sliced operand of a valid slice expression is a <code>nil</code> slice, the result
-is a <code>nil</code> slice. Otherwise, if the result is a slice, it shares its underlying
-array with the operand.
-</p>
-
-<pre>
-var a [10]int
-s1 := a[3:7] // underlying array of s1 is array a; &s1[2] == &a[5]
-s2 := s1[1:4] // underlying array of s2 is underlying array of s1 which is array a; &s2[1] == &a[5]
-s2[1] = 42 // s2[1] == s1[2] == a[5] == 42; they all refer to the same underlying array element
-</pre>
-
-
-<h4>Full slice expressions</h4>
-
-<p>
-The primary expression
-</p>
-
-<pre>
-a[low : high : max]
-</pre>
-
-<p>
-constructs a slice of the same type, and with the same length and elements as the simple slice
-expression <code>a[low : high]</code>. Additionally, it controls the resulting slice's capacity
-by setting it to <code>max - low</code>. Only the first index may be omitted; it defaults to 0.
-The <a href="#Core_types">core type</a> of <code>a</code> must be an array, pointer to array,
-or slice (but not a string).
-After slicing the array <code>a</code>
-</p>
-
-<pre>
-a := [5]int{1, 2, 3, 4, 5}
-t := a[1:3:5]
-</pre>
-
-<p>
-the slice <code>t</code> has type <code>[]int</code>, length 2, capacity 4, and elements
-</p>
-
-<pre>
-t[0] == 2
-t[1] == 3
-</pre>
-
-<p>
-As for simple slice expressions, if <code>a</code> is a pointer to an array,
-<code>a[low : high : max]</code> is shorthand for <code>(*a)[low : high : max]</code>.
-If the sliced operand is an array, it must be <a href="#Address_operators">addressable</a>.
-</p>
-
-<p>
-The indices are <i>in range</i> if <code>0 <= low <= high <= max <= cap(a)</code>,
-otherwise they are <i>out of range</i>.
-A <a href="#Constants">constant</a> index must be non-negative and
-<a href="#Representability">representable</a> by a value of type
-<code>int</code>; for arrays, constant indices must also be in range.
-If multiple indices are constant, the constants that are present must be in range relative to each
-other.
-If the indices are out of range at run time, a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<h3 id="Type_assertions">Type assertions</h3>
-
-<p>
-For an expression <code>x</code> of <a href="#Interface_types">interface type</a>,
-but not a <a href="#Type_parameter_declarations">type parameter</a>, and a type <code>T</code>,
-the primary expression
-</p>
-
-<pre>
-x.(T)
-</pre>
-
-<p>
-asserts that <code>x</code> is not <code>nil</code>
-and that the value stored in <code>x</code> is of type <code>T</code>.
-The notation <code>x.(T)</code> is called a <i>type assertion</i>.
-</p>
-<p>
-More precisely, if <code>T</code> is not an interface type, <code>x.(T)</code> asserts
-that the dynamic type of <code>x</code> is <a href="#Type_identity">identical</a>
-to the type <code>T</code>.
-In this case, <code>T</code> must <a href="#Method_sets">implement</a> the (interface) type of <code>x</code>;
-otherwise the type assertion is invalid since it is not possible for <code>x</code>
-to store a value of type <code>T</code>.
-If <code>T</code> is an interface type, <code>x.(T)</code> asserts that the dynamic type
-of <code>x</code> <a href="#Implementing_an_interface">implements</a> the interface <code>T</code>.
-</p>
-<p>
-If the type assertion holds, the value of the expression is the value
-stored in <code>x</code> and its type is <code>T</code>. If the type assertion is false,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-In other words, even though the dynamic type of <code>x</code>
-is known only at run time, the type of <code>x.(T)</code> is
-known to be <code>T</code> in a correct program.
-</p>
-
-<pre>
-var x interface{} = 7 // x has dynamic type int and value 7
-i := x.(int) // i has type int and value 7
-
-type I interface { m() }
-
-func f(y I) {
- s := y.(string) // illegal: string does not implement I (missing method m)
- r := y.(io.Reader) // r has type io.Reader and the dynamic type of y must implement both I and io.Reader
- …
-}
-</pre>
-
-<p>
-A type assertion used in an <a href="#Assignments">assignment</a> or initialization of the special form
-</p>
-
-<pre>
-v, ok = x.(T)
-v, ok := x.(T)
-var v, ok = x.(T)
-var v, ok interface{} = x.(T) // dynamic types of v and ok are T and bool
-</pre>
-
-<p>
-yields an additional untyped boolean value. The value of <code>ok</code> is <code>true</code>
-if the assertion holds. Otherwise it is <code>false</code> and the value of <code>v</code> is
-the <a href="#The_zero_value">zero value</a> for type <code>T</code>.
-No <a href="#Run_time_panics">run-time panic</a> occurs in this case.
-</p>
-
-
-<h3 id="Calls">Calls</h3>
-
-<p>
-Given an expression <code>f</code> with a <a href="#Core_types">core type</a>
-<code>F</code> of <a href="#Function_types">function type</a>,
-</p>
-
-<pre>
-f(a1, a2, … an)
-</pre>
-
-<p>
-calls <code>f</code> with arguments <code>a1, a2, … an</code>.
-Except for one special case, arguments must be single-valued expressions
-<a href="#Assignability">assignable</a> to the parameter types of
-<code>F</code> and are evaluated before the function is called.
-The type of the expression is the result type
-of <code>F</code>.
-A method invocation is similar but the method itself
-is specified as a selector upon a value of the receiver type for
-the method.
-</p>
-
-<pre>
-math.Atan2(x, y) // function call
-var pt *Point
-pt.Scale(3.5) // method call with receiver pt
-</pre>
-
-<p>
-If <code>f</code> denotes a generic function, it must be
-<a href="#Instantiations">instantiated</a> before it can be called
-or used as a function value.
-</p>
-
-<p>
-In a function call, the function value and arguments are evaluated in
-<a href="#Order_of_evaluation">the usual order</a>.
-After they are evaluated, the parameters of the call are passed by value to the function
-and the called function begins execution.
-The return parameters of the function are passed by value
-back to the caller when the function returns.
-</p>
-
-<p>
-Calling a <code>nil</code> function value
-causes a <a href="#Run_time_panics">run-time panic</a>.
-</p>
-
-<p>
-As a special case, if the return values of a function or method
-<code>g</code> are equal in number and individually
-assignable to the parameters of another function or method
-<code>f</code>, then the call <code>f(g(<i>parameters_of_g</i>))</code>
-will invoke <code>f</code> after binding the return values of
-<code>g</code> to the parameters of <code>f</code> in order. The call
-of <code>f</code> must contain no parameters other than the call of <code>g</code>,
-and <code>g</code> must have at least one return value.
-If <code>f</code> has a final <code>...</code> parameter, it is
-assigned the return values of <code>g</code> that remain after
-assignment of regular parameters.
-</p>
-
-<pre>
-func Split(s string, pos int) (string, string) {
- return s[0:pos], s[pos:]
-}
-
-func Join(s, t string) string {
- return s + t
-}
-
-if Join(Split(value, len(value)/2)) != value {
- log.Panic("test fails")
-}
-</pre>
-
-<p>
-A method call <code>x.m()</code> is valid if the <a href="#Method_sets">method set</a>
-of (the type of) <code>x</code> contains <code>m</code> and the
-argument list can be assigned to the parameter list of <code>m</code>.
-If <code>x</code> is <a href="#Address_operators">addressable</a> and <code>&x</code>'s method
-set contains <code>m</code>, <code>x.m()</code> is shorthand
-for <code>(&x).m()</code>:
-</p>
-
-<pre>
-var p Point
-p.Scale(3.5)
-</pre>
-
-<p>
-There is no distinct method type and there are no method literals.
-</p>
-
-<h3 id="Passing_arguments_to_..._parameters">Passing arguments to <code>...</code> parameters</h3>
-
-<p>
-If <code>f</code> is <a href="#Function_types">variadic</a> with a final
-parameter <code>p</code> of type <code>...T</code>, then within <code>f</code>
-the type of <code>p</code> is equivalent to type <code>[]T</code>.
-If <code>f</code> is invoked with no actual arguments for <code>p</code>,
-the value passed to <code>p</code> is <code>nil</code>.
-Otherwise, the value passed is a new slice
-of type <code>[]T</code> with a new underlying array whose successive elements
-are the actual arguments, which all must be <a href="#Assignability">assignable</a>
-to <code>T</code>. The length and capacity of the slice is therefore
-the number of arguments bound to <code>p</code> and may differ for each
-call site.
-</p>
-
-<p>
-Given the function and calls
-</p>
-<pre>
-func Greeting(prefix string, who ...string)
-Greeting("nobody")
-Greeting("hello:", "Joe", "Anna", "Eileen")
-</pre>
-
-<p>
-within <code>Greeting</code>, <code>who</code> will have the value
-<code>nil</code> in the first call, and
-<code>[]string{"Joe", "Anna", "Eileen"}</code> in the second.
-</p>
-
-<p>
-If the final argument is assignable to a slice type <code>[]T</code> and
-is followed by <code>...</code>, it is passed unchanged as the value
-for a <code>...T</code> parameter. In this case no new slice is created.
-</p>
-
-<p>
-Given the slice <code>s</code> and call
-</p>
-
-<pre>
-s := []string{"James", "Jasmine"}
-Greeting("goodbye:", s...)
-</pre>
-
-<p>
-within <code>Greeting</code>, <code>who</code> will have the same value as <code>s</code>
-with the same underlying array.
-</p>
-
-<h3 id="Instantiations">Instantiations</h3>
-
-<p>
-A generic function or type is <i>instantiated</i> by substituting <i>type arguments</i>
-for the type parameters.
-Instantiation proceeds in two steps:
-</p>
-
-<ol>
-<li>
-Each type argument is substituted for its corresponding type parameter in the generic
-declaration.
-This substitution happens across the entire function or type declaration,
-including the type parameter list itself and any types in that list.
-</li>
-
-<li>
-After substitution, each type argument must <a href="#Interface_types">implement</a>
-the <a href="#Type_parameter_declarations">constraint</a> (instantiated, if necessary)
-of the corresponding type parameter. Otherwise instantiation fails.
-</li>
-</ol>
-
-<p>
-Instantiating a type results in a new non-generic <a href="#Types">named type</a>;
-instantiating a function produces a new non-generic function.
-</p>
-
-<pre>
-type parameter list type arguments after substitution
-
-[P any] int int implements any
-[S ~[]E, E any] []int, int []int implements ~[]int, int implements any
-[P io.Writer] string illegal: string doesn't implement io.Writer
-</pre>
-
-<p>
-For a generic function, type arguments may be provided explicitly, or they
-may be partially or completely <a href="#Type_inference">inferred</a>.
-A generic function that is is <i>not</i> <a href="#Calls">called</a> requires a
-type argument list for instantiation; if the list is partial, all
-remaining type arguments must be inferrable.
-A generic function that is called may provide a (possibly partial) type
-argument list, or may omit it entirely if the omitted type arguments are
-inferrable from the ordinary (non-type) function arguments.
-</p>
-
-<pre>
-func min[T ~int|~float64](x, y T) T { … }
-
-f := min // illegal: min must be instantiated with type arguments when used without being called
-minInt := min[int] // minInt has type func(x, y int) int
-a := minInt(2, 3) // a has value 2 of type int
-b := min[float64](2.0, 3) // b has value 2.0 of type float64
-c := min(b, -1) // c has value -1.0 of type float64
-</pre>
-
-<p>
-A partial type argument list cannot be empty; at least the first argument must be present.
-The list is a prefix of the full list of type arguments, leaving the remaining arguments
-to be inferred. Loosely speaking, type arguments may be omitted from "right to left".
-</p>
-
-<pre>
-func apply[S ~[]E, E any](s S, f(E) E) S { … }
-
-f0 := apply[] // illegal: type argument list cannot be empty
-f1 := apply[[]int] // type argument for S explicitly provided, type argument for E inferred
-f2 := apply[[]string, string] // both type arguments explicitly provided
-
-var bytes []byte
-r := apply(bytes, func(byte) byte { … }) // both type arguments inferred from the function arguments
-</pre>
-
-<p>
-For a generic type, all type arguments must always be provided explicitly.
-</p>
-
-<h3 id="Type_inference">Type inference</h3>
-
-<p>
-Missing function type arguments may be <i>inferred</i> by a series of steps, described below.
-Each step attempts to use known information to infer additional type arguments.
-Type inference stops as soon as all type arguments are known.
-After type inference is complete, it is still necessary to substitute all type arguments
-for type parameters and verify that each type argument
-<a href="#Implementing_an_interface">implements</a> the relevant constraint;
-it is possible for an inferred type argument to fail to implement a constraint, in which
-case instantiation fails.
-</p>
-
-<p>
-Type inference is based on
-</p>
-
-<ul>
-<li>
- a <a href="#Type_parameter_declarations">type parameter list</a>
-</li>
-<li>
- a substitution map <i>M</i> initialized with the known type arguments, if any
-</li>
-<li>
- a (possibly empty) list of ordinary function arguments (in case of a function call only)
-</li>
-</ul>
-
-<p>
-and then proceeds with the following steps:
-</p>
-
-<ol>
-<li>
- apply <a href="#Function_argument_type_inference"><i>function argument type inference</i></a>
- to all <i>typed</i> ordinary function arguments
-</li>
-<li>
- apply <a href="#Constraint_type_inference"><i>constraint type inference</i></a>
-</li>
-<li>
- apply function argument type inference to all <i>untyped</i> ordinary function arguments
- using the default type for each of the untyped function arguments
-</li>
-<li>
- apply constraint type inference
-</li>
-</ol>
-
-<p>
-If there are no ordinary or untyped function arguments, the respective steps are skipped.
-Constraint type inference is skipped if the previous step didn't infer any new type arguments,
-but it is run at least once if there are missing type arguments.
-</p>
-
-<p>
-The substitution map <i>M</i> is carried through all steps, and each step may add entries to <i>M</i>.
-The process stops as soon as <i>M</i> has a type argument for each type parameter or if an inference step fails.
-If an inference step fails, or if <i>M</i> is still missing type arguments after the last step, type inference fails.
-</p>
-
-<h4 id="Type_unification">Type unification</h4>
-
-<p>
-Type inference is based on <i>type unification</i>. A single unification step
-applies to a <a href="#Type_inference">substitution map</a> and two types, either
-or both of which may be or contain type parameters. The substitution map tracks
-the known (explicitly provided or already inferred) type arguments: the map
-contains an entry <code>P</code> → <code>A</code> for each type
-parameter <code>P</code> and corresponding known type argument <code>A</code>.
-During unification, known type arguments take the place of their corresponding type
-parameters when comparing types. Unification is the process of finding substitution
-map entries that make the two types equivalent.
-</p>
-
-<p>
-For unification, two types that don't contain any type parameters from the current type
-parameter list are <i>equivalent</i>
-if they are identical, or if they are channel types that are identical ignoring channel
-direction, or if their underlying types are equivalent.
-</p>
-
-<p>
-Unification works by comparing the structure of pairs of types: their structure
-disregarding type parameters must be identical, and types other than type parameters
-must be equivalent.
-A type parameter in one type may match any complete subtype in the other type;
-each successful match causes an entry to be added to the substitution map.
-If the structure differs, or types other than type parameters are not equivalent,
-unification fails.
-</p>
-
-<!--
-TODO(gri) Somewhere we need to describe the process of adding an entry to the
- substitution map: if the entry is already present, the type argument
- values are themselves unified.
--->
-
-<p>
-For example, if <code>T1</code> and <code>T2</code> are type parameters,
-<code>[]map[int]bool</code> can be unified with any of the following:
-</p>
-
-<pre>
-[]map[int]bool // types are identical
-T1 // adds T1 → []map[int]bool to substitution map
-[]T1 // adds T1 → map[int]bool to substitution map
-[]map[T1]T2 // adds T1 → int and T2 → bool to substitution map
-</pre>
-
-<p>
-On the other hand, <code>[]map[int]bool</code> cannot be unified with any of
-</p>
-
-<pre>
-int // int is not a slice
-struct{} // a struct is not a slice
-[]struct{} // a struct is not a map
-[]map[T1]string // map element types don't match
-</pre>
-
-<p>
-As an exception to this general rule, because a <a href="#Type_definitions">defined type</a>
-<code>D</code> and a type literal <code>L</code> are never equivalent,
-unification compares the underlying type of <code>D</code> with <code>L</code> instead.
-For example, given the defined type
-</p>
-
-<pre>
-type Vector []float64
-</pre>
-
-<p>
-and the type literal <code>[]E</code>, unification compares <code>[]float64</code> with
-<code>[]E</code> and adds an entry <code>E</code> → <code>float64</code> to
-the substitution map.
-</p>
-
-<h4 id="Function_argument_type_inference">Function argument type inference</h4>
-
-<!-- In this section and the section on constraint type inference we start with examples
-rather than have the examples follow the rules as is customary elsewhere in spec.
-Hopefully this helps building an intuition and makes the rules easier to follow. -->
-
-<p>
-Function argument type inference infers type arguments from function arguments:
-if a function parameter is declared with a type <code>T</code> that uses
-type parameters,
-<a href="#Type_unification">unifying</a> the type of the corresponding
-function argument with <code>T</code> may infer type arguments for the type
-parameters used by <code>T</code>.
-</p>
-
-<p>
-For instance, given the generic function
-</p>
-
-<pre>
-func scale[Number ~int64|~float64|~complex128](v []Number, s Number) []Number
-</pre>
-
-<p>
-and the call
-</p>
-
-<pre>
-var vector []float64
-scaledVector := scale(vector, 42)
-</pre>
-
-<p>
-the type argument for <code>Number</code> can be inferred from the function argument
-<code>vector</code> by unifying the type of <code>vector</code> with the corresponding
-parameter type: <code>[]float64</code> and <code>[]Number</code>
-match in structure and <code>float64</code> matches with <code>Number</code>.
-This adds the entry <code>Number</code> → <code>float64</code> to the
-<a href="#Type_unification">substitution map</a>.
-Untyped arguments, such as the second function argument <code>42</code> here, are ignored
-in the first round of function argument type inference and only considered if there are
-unresolved type parameters left.
-</p>
-
-<p>
-Inference happens in two separate phases; each phase operates on a specific list of
-(parameter, argument) pairs:
-</p>
-
-<ol>
-<li>
- The list <i>Lt</i> contains all (parameter, argument) pairs where the parameter
- type uses type parameters and where the function argument is <i>typed</i>.
-</li>
-<li>
- The list <i>Lu</i> contains all remaining pairs where the parameter type is a single
- type parameter. In this list, the respective function arguments are untyped.
-</li>
-</ol>
-
-<p>
-Any other (parameter, argument) pair is ignored.
-</p>
-
-<p>
-By construction, the arguments of the pairs in <i>Lu</i> are <i>untyped</i> constants
-(or the untyped boolean result of a comparison). And because <a href="#Constants">default types</a>
-of untyped values are always predeclared non-composite types, they can never match against
-a composite type, so it is sufficient to only consider parameter types that are single type
-parameters.
-</p>
-
-<p>
-Each list is processed in a separate phase:
-</p>
-
-<ol>
-<li>
- In the first phase, the parameter and argument types of each pair in <i>Lt</i>
- are unified. If unification succeeds for a pair, it may yield new entries that
- are added to the substitution map <i>M</i>. If unification fails, type inference
- fails.
-</li>
-<li>
- The second phase considers the entries of list <i>Lu</i>. Type parameters for
- which the type argument has already been determined are ignored in this phase.
- For each remaining pair, the parameter type (which is a single type parameter) and
- the <a href="#Constants">default type</a> of the corresponding untyped argument is
- unified. If unification fails, type inference fails.
-</li>
-</ol>
-
-<p>
-While unification is successful, processing of each list continues until all list elements
-are considered, even if all type arguments are inferred before the last list element has
-been processed.
-</p>
-
-<p>
-Example:
-</p>
-
-<pre>
-func min[T ~int|~float64](x, y T) T
-
-var x int
-min(x, 2.0) // T is int, inferred from typed argument x; 2.0 is assignable to int
-min(1.0, 2.0) // T is float64, inferred from default type for 1.0 and matches default type for 2.0
-min(1.0, 2) // illegal: default type float64 (for 1.0) doesn't match default type int (for 2)
-</pre>
-
-<p>
-In the example <code>min(1.0, 2)</code>, processing the function argument <code>1.0</code>
-yields the substitution map entry <code>T</code> → <code>float64</code>. Because
-processing continues until all untyped arguments are considered, an error is reported. This
-ensures that type inference does not depend on the order of the untyped arguments.
-</p>
-
-<h4 id="Constraint_type_inference">Constraint type inference</h4>
-
-<p>
-Constraint type inference infers type arguments by considering type constraints.
-If a type parameter <code>P</code> has a constraint with a
-<a href="#Core_types">core type</a> <code>C</code>,
-<a href="#Type_unification">unifying</a> <code>P</code> with <code>C</code>
-may infer additional type arguments, either the type argument for <code>P</code>,
-or if that is already known, possibly the type arguments for type parameters
-used in <code>C</code>.
-</p>
-
-<p>
-For instance, consider the type parameter list with type parameters <code>List</code> and
-<code>Elem</code>:
-</p>
-
-<pre>
-[List ~[]Elem, Elem any]
-</pre>
-
-<p>
-Constraint type inference can deduce the type of <code>Elem</code> from the type argument
-for <code>List</code> because <code>Elem</code> is a type parameter in the core type
-<code>[]Elem</code> of <code>List</code>.
-If the type argument is <code>Bytes</code>:
-</p>
-
-<pre>
-type Bytes []byte
-</pre>
-
-<p>
-unifying the underlying type of <code>Bytes</code> with the core type means
-unifying <code>[]byte</code> with <code>[]Elem</code>. That unification succeeds and yields
-the <a href="#Type_unification">substitution map</a> entry
-<code>Elem</code> → <code>byte</code>.
-Thus, in this example, constraint type inference can infer the second type argument from the
-first one.
-</p>
-
-<p>
-Using the core type of a constraint may lose some information: In the (unlikely) case that
-the constraint's type set contains a single <a href="#Type_definitions">defined type</a>
-<code>N</code>, the corresponding core type is <code>N</code>'s underlying type rather than
-<code>N</code> itself. In this case, constraint type inference may succeed but instantiation
-will fail because the inferred type is not in the type set of the constraint.
-Thus, constraint type inference uses the <i>adjusted core type</i> of
-a constraint: if the type set contains a single type, use that type; otherwise use the
-constraint's core type.
-</p>
-
-<p>
-Generally, constraint type inference proceeds in two phases: Starting with a given
-substitution map <i>M</i>
-</p>
-
-<ol>
-<li>
-For all type parameters with an adjusted core type, unify the type parameter with that
-type. If any unification fails, constraint type inference fails.
-</li>
-
-<li>
-At this point, some entries in <i>M</i> may map type parameters to other
-type parameters or to types containing type parameters. For each entry
-<code>P</code> → <code>A</code> in <i>M</i> where <code>A</code> is or
-contains type parameters <code>Q</code> for which there exist entries
-<code>Q</code> → <code>B</code> in <i>M</i>, substitute those
-<code>Q</code> with the respective <code>B</code> in <code>A</code>.
-Stop when no further substitution is possible.
-</li>
-</ol>
-
-<p>
-The result of constraint type inference is the final substitution map <i>M</i> from type
-parameters <code>P</code> to type arguments <code>A</code> where no type parameter <code>P</code>
-appears in any of the <code>A</code>.
-</p>
-
-<p>
-For instance, given the type parameter list
-</p>
-
-<pre>
-[A any, B []C, C *A]
-</pre>
-
-<p>
-and the single provided type argument <code>int</code> for type parameter <code>A</code>,
-the initial substitution map <i>M</i> contains the entry <code>A</code> → <code>int</code>.
-</p>
-
-<p>
-In the first phase, the type parameters <code>B</code> and <code>C</code> are unified
-with the core type of their respective constraints. This adds the entries
-<code>B</code> → <code>[]C</code> and <code>C</code> → <code>*A</code>
-to <i>M</i>.
-
-<p>
-At this point there are two entries in <i>M</i> where the right-hand side
-is or contains type parameters for which there exists other entries in <i>M</i>:
-<code>[]C</code> and <code>*A</code>.
-In the second phase, these type parameters are replaced with their respective
-types. It doesn't matter in which order this happens. Starting with the state
-of <i>M</i> after the first phase:
-</p>
-
-<p>
-<code>A</code> → <code>int</code>,
-<code>B</code> → <code>[]C</code>,
-<code>C</code> → <code>*A</code>
-</p>
-
-<p>
-Replace <code>A</code> on the right-hand side of → with <code>int</code>:
-</p>
-
-<p>
-<code>A</code> → <code>int</code>,
-<code>B</code> → <code>[]C</code>,
-<code>C</code> → <code>*int</code>
-</p>
-
-<p>
-Replace <code>C</code> on the right-hand side of → with <code>*int</code>:
-</p>
-
-<p>
-<code>A</code> → <code>int</code>,
-<code>B</code> → <code>[]*int</code>,
-<code>C</code> → <code>*int</code>
-</p>
-
-<p>
-At this point no further substitution is possible and the map is full.
-Therefore, <code>M</code> represents the final map of type parameters
-to type arguments for the given type parameter list.
-</p>
-
-<h3 id="Operators">Operators</h3>
-
-<p>
-Operators combine operands into expressions.
-</p>
-
-<pre class="ebnf">
-Expression = UnaryExpr | Expression binary_op Expression .
-UnaryExpr = PrimaryExpr | unary_op UnaryExpr .
-
-binary_op = "||" | "&&" | rel_op | add_op | mul_op .
-rel_op = "==" | "!=" | "<" | "<=" | ">" | ">=" .
-add_op = "+" | "-" | "|" | "^" .
-mul_op = "*" | "/" | "%" | "<<" | ">>" | "&" | "&^" .
-
-unary_op = "+" | "-" | "!" | "^" | "*" | "&" | "<-" .
-</pre>
-
-<p>
-Comparisons are discussed <a href="#Comparison_operators">elsewhere</a>.
-For other binary operators, the operand types must be <a href="#Type_identity">identical</a>
-unless the operation involves shifts or untyped <a href="#Constants">constants</a>.
-For operations involving constants only, see the section on
-<a href="#Constant_expressions">constant expressions</a>.
-</p>
-
-<p>
-Except for shift operations, if one operand is an untyped <a href="#Constants">constant</a>
-and the other operand is not, the constant is implicitly <a href="#Conversions">converted</a>
-to the type of the other operand.
-</p>
-
-<p>
-The right operand in a shift expression must have <a href="#Numeric_types">integer type</a>
-or be an untyped constant <a href="#Representability">representable</a> by a
-value of type <code>uint</code>.
-If the left operand of a non-constant shift expression is an untyped constant,
-it is first implicitly converted to the type it would assume if the shift expression were
-replaced by its left operand alone.
-</p>
-
-<pre>
-var a [1024]byte
-var s uint = 33
-
-// The results of the following examples are given for 64-bit ints.
-var i = 1<<s // 1 has type int
-var j int32 = 1<<s // 1 has type int32; j == 0
-var k = uint64(1<<s) // 1 has type uint64; k == 1<<33
-var m int = 1.0<<s // 1.0 has type int; m == 1<<33
-var n = 1.0<<s == j // 1.0 has type int32; n == true
-var o = 1<<s == 2<<s // 1 and 2 have type int; o == false
-var p = 1<<s == 1<<33 // 1 has type int; p == true
-var u = 1.0<<s // illegal: 1.0 has type float64, cannot shift
-var u1 = 1.0<<s != 0 // illegal: 1.0 has type float64, cannot shift
-var u2 = 1<<s != 1.0 // illegal: 1 has type float64, cannot shift
-var v1 float32 = 1<<s // illegal: 1 has type float32, cannot shift
-var v2 = string(1<<s) // illegal: 1 is converted to a string, cannot shift
-var w int64 = 1.0<<33 // 1.0<<33 is a constant shift expression; w == 1<<33
-var x = a[1.0<<s] // panics: 1.0 has type int, but 1<<33 overflows array bounds
-var b = make([]byte, 1.0<<s) // 1.0 has type int; len(b) == 1<<33
-
-// The results of the following examples are given for 32-bit ints,
-// which means the shifts will overflow.
-var mm int = 1.0<<s // 1.0 has type int; mm == 0
-var oo = 1<<s == 2<<s // 1 and 2 have type int; oo == true
-var pp = 1<<s == 1<<33 // illegal: 1 has type int, but 1<<33 overflows int
-var xx = a[1.0<<s] // 1.0 has type int; xx == a[0]
-var bb = make([]byte, 1.0<<s) // 1.0 has type int; len(bb) == 0
-</pre>
-
-<h4 id="Operator_precedence">Operator precedence</h4>
-<p>
-Unary operators have the highest precedence.
-As the <code>++</code> and <code>--</code> operators form
-statements, not expressions, they fall
-outside the operator hierarchy.
-As a consequence, statement <code>*p++</code> is the same as <code>(*p)++</code>.
-<p>
-There are five precedence levels for binary operators.
-Multiplication operators bind strongest, followed by addition
-operators, comparison operators, <code>&&</code> (logical AND),
-and finally <code>||</code> (logical OR):
-</p>
-
-<pre class="grammar">
-Precedence Operator
- 5 * / % << >> & &^
- 4 + - | ^
- 3 == != < <= > >=
- 2 &&
- 1 ||
-</pre>
-
-<p>
-Binary operators of the same precedence associate from left to right.
-For instance, <code>x / y * z</code> is the same as <code>(x / y) * z</code>.
-</p>
-
-<pre>
-+x
-23 + 3*x[i]
-x <= f()
-^a >> b
-f() || g()
-x == y+1 && <-chanInt > 0
-</pre>
-
-
-<h3 id="Arithmetic_operators">Arithmetic operators</h3>
-<p>
-Arithmetic operators apply to numeric values and yield a result of the same
-type as the first operand. The four standard arithmetic operators (<code>+</code>,
-<code>-</code>, <code>*</code>, <code>/</code>) apply to
-<a href="#Numeric_types">integer</a>, <a href="#Numeric_types">floating-point</a>, and
-<a href="#Numeric_types">complex</a> types; <code>+</code> also applies to <a href="#String_types">strings</a>.
-The bitwise logical and shift operators apply to integers only.
-</p>
-
-<pre class="grammar">
-+ sum integers, floats, complex values, strings
-- difference integers, floats, complex values
-* product integers, floats, complex values
-/ quotient integers, floats, complex values
-% remainder integers
-
-& bitwise AND integers
-| bitwise OR integers
-^ bitwise XOR integers
-&^ bit clear (AND NOT) integers
-
-<< left shift integer << integer >= 0
->> right shift integer >> integer >= 0
-</pre>
-
-<p>
-If the operand type is a <a href="#Type_parameter_declarations">type parameter</a>,
-the operator must apply to each type in that type set.
-The operands are represented as values of the type argument that the type parameter
-is <a href="#Instantiations">instantiated</a> with, and the operation is computed
-with the precision of that type argument. For example, given the function:
-</p>
-
-<pre>
-func dotProduct[F ~float32|~float64](v1, v2 []F) F {
- var s F
- for i, x := range v1 {
- y := v2[i]
- s += x * y
- }
- return s
-}
-</pre>
-
-<p>
-the product <code>x * y</code> and the addition <code>s += x * y</code>
-are computed with <code>float32</code> or <code>float64</code> precision,
-respectively, depending on the type argument for <code>F</code>.
-</p>
-
-<h4 id="Integer_operators">Integer operators</h4>
-
-<p>
-For two integer values <code>x</code> and <code>y</code>, the integer quotient
-<code>q = x / y</code> and remainder <code>r = x % y</code> satisfy the following
-relationships:
-</p>
-
-<pre>
-x = q*y + r and |r| < |y|
-</pre>
-
-<p>
-with <code>x / y</code> truncated towards zero
-(<a href="https://en.wikipedia.org/wiki/Modulo_operation">"truncated division"</a>).
-</p>
-
-<pre>
- x y x / y x % y
- 5 3 1 2
--5 3 -1 -2
- 5 -3 -1 2
--5 -3 1 -2
-</pre>
-
-<p>
-The one exception to this rule is that if the dividend <code>x</code> is
-the most negative value for the int type of <code>x</code>, the quotient
-<code>q = x / -1</code> is equal to <code>x</code> (and <code>r = 0</code>)
-due to two's-complement <a href="#Integer_overflow">integer overflow</a>:
-</p>
-
-<pre>
- x, q
-int8 -128
-int16 -32768
-int32 -2147483648
-int64 -9223372036854775808
-</pre>
-
-<p>
-If the divisor is a <a href="#Constants">constant</a>, it must not be zero.
-If the divisor is zero at run time, a <a href="#Run_time_panics">run-time panic</a> occurs.
-If the dividend is non-negative and the divisor is a constant power of 2,
-the division may be replaced by a right shift, and computing the remainder may
-be replaced by a bitwise AND operation:
-</p>
-
-<pre>
- x x / 4 x % 4 x >> 2 x & 3
- 11 2 3 2 3
--11 -2 -3 -3 1
-</pre>
-
-<p>
-The shift operators shift the left operand by the shift count specified by the
-right operand, which must be non-negative. If the shift count is negative at run time,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-The shift operators implement arithmetic shifts if the left operand is a signed
-integer and logical shifts if it is an unsigned integer.
-There is no upper limit on the shift count. Shifts behave
-as if the left operand is shifted <code>n</code> times by 1 for a shift
-count of <code>n</code>.
-As a result, <code>x << 1</code> is the same as <code>x*2</code>
-and <code>x >> 1</code> is the same as
-<code>x/2</code> but truncated towards negative infinity.
-</p>
-
-<p>
-For integer operands, the unary operators
-<code>+</code>, <code>-</code>, and <code>^</code> are defined as
-follows:
-</p>
-
-<pre class="grammar">
-+x is 0 + x
--x negation is 0 - x
-^x bitwise complement is m ^ x with m = "all bits set to 1" for unsigned x
- and m = -1 for signed x
-</pre>
-
-
-<h4 id="Integer_overflow">Integer overflow</h4>
-
-<p>
-For <a href="#Numeric_types">unsigned integer</a> values, the operations <code>+</code>,
-<code>-</code>, <code>*</code>, and <code><<</code> are
-computed modulo 2<sup><i>n</i></sup>, where <i>n</i> is the bit width of
-the unsigned integer's type.
-Loosely speaking, these unsigned integer operations
-discard high bits upon overflow, and programs may rely on "wrap around".
-</p>
-
-<p>
-For signed integers, the operations <code>+</code>,
-<code>-</code>, <code>*</code>, <code>/</code>, and <code><<</code> may legally
-overflow and the resulting value exists and is deterministically defined
-by the signed integer representation, the operation, and its operands.
-Overflow does not cause a <a href="#Run_time_panics">run-time panic</a>.
-A compiler may not optimize code under the assumption that overflow does
-not occur. For instance, it may not assume that <code>x < x + 1</code> is always true.
-</p>
-
-<h4 id="Floating_point_operators">Floating-point operators</h4>
-
-<p>
-For floating-point and complex numbers,
-<code>+x</code> is the same as <code>x</code>,
-while <code>-x</code> is the negation of <code>x</code>.
-The result of a floating-point or complex division by zero is not specified beyond the
-IEEE-754 standard; whether a <a href="#Run_time_panics">run-time panic</a>
-occurs is implementation-specific.
-</p>
-
-<p>
-An implementation may combine multiple floating-point operations into a single
-fused operation, possibly across statements, and produce a result that differs
-from the value obtained by executing and rounding the instructions individually.
-An explicit <a href="#Numeric_types">floating-point type</a> <a href="#Conversions">conversion</a> rounds to
-the precision of the target type, preventing fusion that would discard that rounding.
-</p>
-
-<p>
-For instance, some architectures provide a "fused multiply and add" (FMA) instruction
-that computes <code>x*y + z</code> without rounding the intermediate result <code>x*y</code>.
-These examples show when a Go implementation can use that instruction:
-</p>
-
-<pre>
-// FMA allowed for computing r, because x*y is not explicitly rounded:
-r = x*y + z
-r = z; r += x*y
-t = x*y; r = t + z
-*p = x*y; r = *p + z
-r = x*y + float64(z)
-
-// FMA disallowed for computing r, because it would omit rounding of x*y:
-r = float64(x*y) + z
-r = z; r += float64(x*y)
-t = float64(x*y); r = t + z
-</pre>
-
-<h4 id="String_concatenation">String concatenation</h4>
-
-<p>
-Strings can be concatenated using the <code>+</code> operator
-or the <code>+=</code> assignment operator:
-</p>
-
-<pre>
-s := "hi" + string(c)
-s += " and good bye"
-</pre>
-
-<p>
-String addition creates a new string by concatenating the operands.
-</p>
-
-<h3 id="Comparison_operators">Comparison operators</h3>
-
-<p>
-Comparison operators compare two operands and yield an untyped boolean value.
-</p>
-
-<pre class="grammar">
-== equal
-!= not equal
-< less
-<= less or equal
-> greater
->= greater or equal
-</pre>
-
-<p>
-In any comparison, the first operand
-must be <a href="#Assignability">assignable</a>
-to the type of the second operand, or vice versa.
-</p>
-<p>
-The equality operators <code>==</code> and <code>!=</code> apply
-to operands that are <i>comparable</i>.
-The ordering operators <code><</code>, <code><=</code>, <code>></code>, and <code>>=</code>
-apply to operands that are <i>ordered</i>.
-These terms and the result of the comparisons are defined as follows:
-</p>
-
-<ul>
- <li>
- Boolean values are comparable.
- Two boolean values are equal if they are either both
- <code>true</code> or both <code>false</code>.
- </li>
-
- <li>
- Integer values are comparable and ordered, in the usual way.
- </li>
-
- <li>
- Floating-point values are comparable and ordered,
- as defined by the IEEE-754 standard.
- </li>
-
- <li>
- Complex values are comparable.
- Two complex values <code>u</code> and <code>v</code> are
- equal if both <code>real(u) == real(v)</code> and
- <code>imag(u) == imag(v)</code>.
- </li>
-
- <li>
- String values are comparable and ordered, lexically byte-wise.
- </li>
-
- <li>
- Pointer values are comparable.
- Two pointer values are equal if they point to the same variable or if both have value <code>nil</code>.
- Pointers to distinct <a href="#Size_and_alignment_guarantees">zero-size</a> variables may or may not be equal.
- </li>
-
- <li>
- Channel values are comparable.
- Two channel values are equal if they were created by the same call to
- <a href="#Making_slices_maps_and_channels"><code>make</code></a>
- or if both have value <code>nil</code>.
- </li>
-
- <li>
- Interface values are comparable.
- Two interface values are equal if they have <a href="#Type_identity">identical</a> dynamic types
- and equal dynamic values or if both have value <code>nil</code>.
- </li>
-
- <li>
- A value <code>x</code> of non-interface type <code>X</code> and
- a value <code>t</code> of interface type <code>T</code> are comparable when values
- of type <code>X</code> are comparable and
- <code>X</code> <a href="#Implementing_an_interface">implements</a> <code>T</code>.
- They are equal if <code>t</code>'s dynamic type is identical to <code>X</code>
- and <code>t</code>'s dynamic value is equal to <code>x</code>.
- </li>
-
- <li>
- Struct values are comparable if all their fields are comparable.
- Two struct values are equal if their corresponding
- non-<a href="#Blank_identifier">blank</a> fields are equal.
- </li>
-
- <li>
- Array values are comparable if values of the array element type are comparable.
- Two array values are equal if their corresponding elements are equal.
- </li>
-</ul>
-
-<p>
-A comparison of two interface values with identical dynamic types
-causes a <a href="#Run_time_panics">run-time panic</a> if values
-of that type are not comparable. This behavior applies not only to direct interface
-value comparisons but also when comparing arrays of interface values
-or structs with interface-valued fields.
-</p>
-
-<p>
-Slice, map, and function values are not comparable.
-However, as a special case, a slice, map, or function value may
-be compared to the predeclared identifier <code>nil</code>.
-Comparison of pointer, channel, and interface values to <code>nil</code>
-is also allowed and follows from the general rules above.
-</p>
-
-<pre>
-const c = 3 < 4 // c is the untyped boolean constant true
-
-type MyBool bool
-var x, y int
-var (
- // The result of a comparison is an untyped boolean.
- // The usual assignment rules apply.
- b3 = x == y // b3 has type bool
- b4 bool = x == y // b4 has type bool
- b5 MyBool = x == y // b5 has type MyBool
-)
-</pre>
-
-<h3 id="Logical_operators">Logical operators</h3>
-
-<p>
-Logical operators apply to <a href="#Boolean_types">boolean</a> values
-and yield a result of the same type as the operands.
-The right operand is evaluated conditionally.
-</p>
-
-<pre class="grammar">
-&& conditional AND p && q is "if p then q else false"
-|| conditional OR p || q is "if p then true else q"
-! NOT !p is "not p"
-</pre>
-
-
-<h3 id="Address_operators">Address operators</h3>
-
-<p>
-For an operand <code>x</code> of type <code>T</code>, the address operation
-<code>&x</code> generates a pointer of type <code>*T</code> to <code>x</code>.
-The operand must be <i>addressable</i>,
-that is, either a variable, pointer indirection, or slice indexing
-operation; or a field selector of an addressable struct operand;
-or an array indexing operation of an addressable array.
-As an exception to the addressability requirement, <code>x</code> may also be a
-(possibly parenthesized)
-<a href="#Composite_literals">composite literal</a>.
-If the evaluation of <code>x</code> would cause a <a href="#Run_time_panics">run-time panic</a>,
-then the evaluation of <code>&x</code> does too.
-</p>
-
-<p>
-For an operand <code>x</code> of pointer type <code>*T</code>, the pointer
-indirection <code>*x</code> denotes the <a href="#Variables">variable</a> of type <code>T</code> pointed
-to by <code>x</code>.
-If <code>x</code> is <code>nil</code>, an attempt to evaluate <code>*x</code>
-will cause a <a href="#Run_time_panics">run-time panic</a>.
-</p>
-
-<pre>
-&x
-&a[f(2)]
-&Point{2, 3}
-*p
-*pf(x)
-
-var x *int = nil
-*x // causes a run-time panic
-&*x // causes a run-time panic
-</pre>
-
-
-<h3 id="Receive_operator">Receive operator</h3>
-
-<p>
-For an operand <code>ch</code> whose <a href="#Core_types">core type</a> is a
-<a href="#Channel_types">channel</a>,
-the value of the receive operation <code><-ch</code> is the value received
-from the channel <code>ch</code>. The channel direction must permit receive operations,
-and the type of the receive operation is the element type of the channel.
-The expression blocks until a value is available.
-Receiving from a <code>nil</code> channel blocks forever.
-A receive operation on a <a href="#Close">closed</a> channel can always proceed
-immediately, yielding the element type's <a href="#The_zero_value">zero value</a>
-after any previously sent values have been received.
-</p>
-
-<pre>
-v1 := <-ch
-v2 = <-ch
-f(<-ch)
-<-strobe // wait until clock pulse and discard received value
-</pre>
-
-<p>
-A receive expression used in an <a href="#Assignments">assignment</a> or initialization of the special form
-</p>
-
-<pre>
-x, ok = <-ch
-x, ok := <-ch
-var x, ok = <-ch
-var x, ok T = <-ch
-</pre>
-
-<p>
-yields an additional untyped boolean result reporting whether the
-communication succeeded. The value of <code>ok</code> is <code>true</code>
-if the value received was delivered by a successful send operation to the
-channel, or <code>false</code> if it is a zero value generated because the
-channel is closed and empty.
-</p>
-
-
-<h3 id="Conversions">Conversions</h3>
-
-<p>
-A conversion changes the <a href="#Types">type</a> of an expression
-to the type specified by the conversion.
-A conversion may appear literally in the source, or it may be <i>implied</i>
-by the context in which an expression appears.
-</p>
-
-<p>
-An <i>explicit</i> conversion is an expression of the form <code>T(x)</code>
-where <code>T</code> is a type and <code>x</code> is an expression
-that can be converted to type <code>T</code>.
-</p>
-
-<pre class="ebnf">
-Conversion = Type "(" Expression [ "," ] ")" .
-</pre>
-
-<p>
-If the type starts with the operator <code>*</code> or <code><-</code>,
-or if the type starts with the keyword <code>func</code>
-and has no result list, it must be parenthesized when
-necessary to avoid ambiguity:
-</p>
-
-<pre>
-*Point(p) // same as *(Point(p))
-(*Point)(p) // p is converted to *Point
-<-chan int(c) // same as <-(chan int(c))
-(<-chan int)(c) // c is converted to <-chan int
-func()(x) // function signature func() x
-(func())(x) // x is converted to func()
-(func() int)(x) // x is converted to func() int
-func() int(x) // x is converted to func() int (unambiguous)
-</pre>
-
-<p>
-A <a href="#Constants">constant</a> value <code>x</code> can be converted to
-type <code>T</code> if <code>x</code> is <a href="#Representability">representable</a>
-by a value of <code>T</code>.
-As a special case, an integer constant <code>x</code> can be explicitly converted to a
-<a href="#String_types">string type</a> using the
-<a href="#Conversions_to_and_from_a_string_type">same rule</a>
-as for non-constant <code>x</code>.
-</p>
-
-<p>
-Converting a constant to a type that is not a <a href="#Type_parameter_declarations">type parameter</a>
-yields a typed constant.
-</p>
-
-<pre>
-uint(iota) // iota value of type uint
-float32(2.718281828) // 2.718281828 of type float32
-complex128(1) // 1.0 + 0.0i of type complex128
-float32(0.49999999) // 0.5 of type float32
-float64(-1e-1000) // 0.0 of type float64
-string('x') // "x" of type string
-string(0x266c) // "♬" of type string
-MyString("foo" + "bar") // "foobar" of type MyString
-string([]byte{'a'}) // not a constant: []byte{'a'} is not a constant
-(*int)(nil) // not a constant: nil is not a constant, *int is not a boolean, numeric, or string type
-int(1.2) // illegal: 1.2 cannot be represented as an int
-string(65.0) // illegal: 65.0 is not an integer constant
-</pre>
-
-<p>
-Converting a constant to a type parameter yields a <i>non-constant</i> value of that type,
-with the value represented as a value of the type argument that the type parameter
-is <a href="#Instantiations">instantiated</a> with.
-For example, given the function:
-</p>
-
-<pre>
-func f[P ~float32|~float64]() {
- … P(1.1) …
-}
-</pre>
-
-<p>
-the conversion <code>P(1.1)</code> results in a non-constant value of type <code>P</code>
-and the value <code>1.1</code> is represented as a <code>float32</code> or a <code>float64</code>
-depending on the type argument for <code>f</code>.
-Accordingly, if <code>f</code> is instantiated with a <code>float32</code> type,
-the numeric value of the expression <code>P(1.1) + 1.2</code> will be computed
-with the same precision as the corresponding non-constant <code>float32</code>
-addition.
-</p>
-
-<p>
-A non-constant value <code>x</code> can be converted to type <code>T</code>
-in any of these cases:
-</p>
-
-<ul>
- <li>
- <code>x</code> is <a href="#Assignability">assignable</a>
- to <code>T</code>.
- </li>
- <li>
- ignoring struct tags (see below),
- <code>x</code>'s type and <code>T</code> are not
- <a href="#Type_parameter_declarations">type parameters</a> but have
- <a href="#Type_identity">identical</a> <a href="#Types">underlying types</a>.
- </li>
- <li>
- ignoring struct tags (see below),
- <code>x</code>'s type and <code>T</code> are pointer types
- that are not <a href="#Types">named types</a>,
- and their pointer base types are not type parameters but
- have identical underlying types.
- </li>
- <li>
- <code>x</code>'s type and <code>T</code> are both integer or floating
- point types.
- </li>
- <li>
- <code>x</code>'s type and <code>T</code> are both complex types.
- </li>
- <li>
- <code>x</code> is an integer or a slice of bytes or runes
- and <code>T</code> is a string type.
- </li>
- <li>
- <code>x</code> is a string and <code>T</code> is a slice of bytes or runes.
- </li>
- <li>
- <code>x</code> is a slice, <code>T</code> is a pointer to an array,
- and the slice and array types have <a href="#Type_identity">identical</a> element types.
- </li>
-</ul>
-
-<p>
-Additionally, if <code>T</code> or <code>x</code>'s type <code>V</code> are type
-parameters, <code>x</code>
-can also be converted to type <code>T</code> if one of the following conditions applies:
-</p>
-
-<ul>
-<li>
-Both <code>V</code> and <code>T</code> are type parameters and a value of each
-type in <code>V</code>'s type set can be converted to each type in <code>T</code>'s
-type set.
-</li>
-<li>
-Only <code>V</code> is a type parameter and a value of each
-type in <code>V</code>'s type set can be converted to <code>T</code>.
-</li>
-<li>
-Only <code>T</code> is a type parameter and <code>x</code> can be converted to each
-type in <code>T</code>'s type set.
-</li>
-</ul>
-
-<p>
-<a href="#Struct_types">Struct tags</a> are ignored when comparing struct types
-for identity for the purpose of conversion:
-</p>
-
-<pre>
-type Person struct {
- Name string
- Address *struct {
- Street string
- City string
- }
-}
-
-var data *struct {
- Name string `json:"name"`
- Address *struct {
- Street string `json:"street"`
- City string `json:"city"`
- } `json:"address"`
-}
-
-var person = (*Person)(data) // ignoring tags, the underlying types are identical
-</pre>
-
-<p>
-Specific rules apply to (non-constant) conversions between numeric types or
-to and from a string type.
-These conversions may change the representation of <code>x</code>
-and incur a run-time cost.
-All other conversions only change the type but not the representation
-of <code>x</code>.
-</p>
-
-<p>
-There is no linguistic mechanism to convert between pointers and integers.
-The package <a href="#Package_unsafe"><code>unsafe</code></a>
-implements this functionality under restricted circumstances.
-</p>
-
-<h4>Conversions between numeric types</h4>
-
-<p>
-For the conversion of non-constant numeric values, the following rules apply:
-</p>
-
-<ol>
-<li>
-When converting between <a href="#Numeric_types">integer types</a>, if the value is a signed integer, it is
-sign extended to implicit infinite precision; otherwise it is zero extended.
-It is then truncated to fit in the result type's size.
-For example, if <code>v := uint16(0x10F0)</code>, then <code>uint32(int8(v)) == 0xFFFFFFF0</code>.
-The conversion always yields a valid value; there is no indication of overflow.
-</li>
-<li>
-When converting a <a href="#Numeric_types">floating-point number</a> to an integer, the fraction is discarded
-(truncation towards zero).
-</li>
-<li>
-When converting an integer or floating-point number to a floating-point type,
-or a <a href="#Numeric_types">complex number</a> to another complex type, the result value is rounded
-to the precision specified by the destination type.
-For instance, the value of a variable <code>x</code> of type <code>float32</code>
-may be stored using additional precision beyond that of an IEEE-754 32-bit number,
-but float32(x) represents the result of rounding <code>x</code>'s value to
-32-bit precision. Similarly, <code>x + 0.1</code> may use more than 32 bits
-of precision, but <code>float32(x + 0.1)</code> does not.
-</li>
-</ol>
-
-<p>
-In all non-constant conversions involving floating-point or complex values,
-if the result type cannot represent the value the conversion
-succeeds but the result value is implementation-dependent.
-</p>
-
-<h4 id="Conversions_to_and_from_a_string_type">Conversions to and from a string type</h4>
-
-<ol>
-<li>
-Converting a signed or unsigned integer value to a string type yields a
-string containing the UTF-8 representation of the integer. Values outside
-the range of valid Unicode code points are converted to <code>"\uFFFD"</code>.
-
-<pre>
-string('a') // "a"
-string(-1) // "\ufffd" == "\xef\xbf\xbd"
-string(0xf8) // "\u00f8" == "ø" == "\xc3\xb8"
-type MyString string
-MyString(0x65e5) // "\u65e5" == "日" == "\xe6\x97\xa5"
-</pre>
-</li>
-
-<li>
-Converting a slice of bytes to a string type yields
-a string whose successive bytes are the elements of the slice.
-
-<pre>
-string([]byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}) // "hellø"
-string([]byte{}) // ""
-string([]byte(nil)) // ""
-
-type MyBytes []byte
-string(MyBytes{'h', 'e', 'l', 'l', '\xc3', '\xb8'}) // "hellø"
-</pre>
-</li>
-
-<li>
-Converting a slice of runes to a string type yields
-a string that is the concatenation of the individual rune values
-converted to strings.
-
-<pre>
-string([]rune{0x767d, 0x9d6c, 0x7fd4}) // "\u767d\u9d6c\u7fd4" == "白鵬翔"
-string([]rune{}) // ""
-string([]rune(nil)) // ""
-
-type MyRunes []rune
-string(MyRunes{0x767d, 0x9d6c, 0x7fd4}) // "\u767d\u9d6c\u7fd4" == "白鵬翔"
-</pre>
-</li>
-
-<li>
-Converting a value of a string type to a slice of bytes type
-yields a slice whose successive elements are the bytes of the string.
-
-<pre>
-[]byte("hellø") // []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}
-[]byte("") // []byte{}
-
-MyBytes("hellø") // []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}
-</pre>
-</li>
-
-<li>
-Converting a value of a string type to a slice of runes type
-yields a slice containing the individual Unicode code points of the string.
-
-<pre>
-[]rune(MyString("白鵬翔")) // []rune{0x767d, 0x9d6c, 0x7fd4}
-[]rune("") // []rune{}
-
-MyRunes("白鵬翔") // []rune{0x767d, 0x9d6c, 0x7fd4}
-</pre>
-</li>
-</ol>
-
-<h4 id="Conversions_from_slice_to_array_pointer">Conversions from slice to array pointer</h4>
-
-<p>
-Converting a slice to an array pointer yields a pointer to the underlying array of the slice.
-If the <a href="#Length_and_capacity">length</a> of the slice is less than the length of the array,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<pre>
-s := make([]byte, 2, 4)
-s0 := (*[0]byte)(s) // s0 != nil
-s1 := (*[1]byte)(s[1:]) // &s1[0] == &s[1]
-s2 := (*[2]byte)(s) // &s2[0] == &s[0]
-s4 := (*[4]byte)(s) // panics: len([4]byte) > len(s)
-
-var t []string
-t0 := (*[0]string)(t) // t0 == nil
-t1 := (*[1]string)(t) // panics: len([1]string) > len(t)
-
-u := make([]byte, 0)
-u0 := (*[0]byte)(u) // u0 != nil
-</pre>
-
-<h3 id="Constant_expressions">Constant expressions</h3>
-
-<p>
-Constant expressions may contain only <a href="#Constants">constant</a>
-operands and are evaluated at compile time.
-</p>
-
-<p>
-Untyped boolean, numeric, and string constants may be used as operands
-wherever it is legal to use an operand of boolean, numeric, or string type,
-respectively.
-</p>
-
-<p>
-A constant <a href="#Comparison_operators">comparison</a> always yields
-an untyped boolean constant. If the left operand of a constant
-<a href="#Operators">shift expression</a> is an untyped constant, the
-result is an integer constant; otherwise it is a constant of the same
-type as the left operand, which must be of
-<a href="#Numeric_types">integer type</a>.
-</p>
-
-<p>
-Any other operation on untyped constants results in an untyped constant of the
-same kind; that is, a boolean, integer, floating-point, complex, or string
-constant.
-If the untyped operands of a binary operation (other than a shift) are of
-different kinds, the result is of the operand's kind that appears later in this
-list: integer, rune, floating-point, complex.
-For example, an untyped integer constant divided by an
-untyped complex constant yields an untyped complex constant.
-</p>
-
-<pre>
-const a = 2 + 3.0 // a == 5.0 (untyped floating-point constant)
-const b = 15 / 4 // b == 3 (untyped integer constant)
-const c = 15 / 4.0 // c == 3.75 (untyped floating-point constant)
-const Θ float64 = 3/2 // Θ == 1.0 (type float64, 3/2 is integer division)
-const Π float64 = 3/2. // Π == 1.5 (type float64, 3/2. is float division)
-const d = 1 << 3.0 // d == 8 (untyped integer constant)
-const e = 1.0 << 3 // e == 8 (untyped integer constant)
-const f = int32(1) << 33 // illegal (constant 8589934592 overflows int32)
-const g = float64(2) >> 1 // illegal (float64(2) is a typed floating-point constant)
-const h = "foo" > "bar" // h == true (untyped boolean constant)
-const j = true // j == true (untyped boolean constant)
-const k = 'w' + 1 // k == 'x' (untyped rune constant)
-const l = "hi" // l == "hi" (untyped string constant)
-const m = string(k) // m == "x" (type string)
-const Σ = 1 - 0.707i // (untyped complex constant)
-const Δ = Σ + 2.0e-4 // (untyped complex constant)
-const Φ = iota*1i - 1/1i // (untyped complex constant)
-</pre>
-
-<p>
-Applying the built-in function <code>complex</code> to untyped
-integer, rune, or floating-point constants yields
-an untyped complex constant.
-</p>
-
-<pre>
-const ic = complex(0, c) // ic == 3.75i (untyped complex constant)
-const iΘ = complex(0, Θ) // iΘ == 1i (type complex128)
-</pre>
-
-<p>
-Constant expressions are always evaluated exactly; intermediate values and the
-constants themselves may require precision significantly larger than supported
-by any predeclared type in the language. The following are legal declarations:
-</p>
-
-<pre>
-const Huge = 1 << 100 // Huge == 1267650600228229401496703205376 (untyped integer constant)
-const Four int8 = Huge >> 98 // Four == 4 (type int8)
-</pre>
-
-<p>
-The divisor of a constant division or remainder operation must not be zero:
-</p>
-
-<pre>
-3.14 / 0.0 // illegal: division by zero
-</pre>
-
-<p>
-The values of <i>typed</i> constants must always be accurately
-<a href="#Representability">representable</a> by values
-of the constant type. The following constant expressions are illegal:
-</p>
-
-<pre>
-uint(-1) // -1 cannot be represented as a uint
-int(3.14) // 3.14 cannot be represented as an int
-int64(Huge) // 1267650600228229401496703205376 cannot be represented as an int64
-Four * 300 // operand 300 cannot be represented as an int8 (type of Four)
-Four * 100 // product 400 cannot be represented as an int8 (type of Four)
-</pre>
-
-<p>
-The mask used by the unary bitwise complement operator <code>^</code> matches
-the rule for non-constants: the mask is all 1s for unsigned constants
-and -1 for signed and untyped constants.
-</p>
-
-<pre>
-^1 // untyped integer constant, equal to -2
-uint8(^1) // illegal: same as uint8(-2), -2 cannot be represented as a uint8
-^uint8(1) // typed uint8 constant, same as 0xFF ^ uint8(1) = uint8(0xFE)
-int8(^1) // same as int8(-2)
-^int8(1) // same as -1 ^ int8(1) = -2
-</pre>
-
-<p>
-Implementation restriction: A compiler may use rounding while
-computing untyped floating-point or complex constant expressions; see
-the implementation restriction in the section
-on <a href="#Constants">constants</a>. This rounding may cause a
-floating-point constant expression to be invalid in an integer
-context, even if it would be integral when calculated using infinite
-precision, and vice versa.
-</p>
-
-
-<h3 id="Order_of_evaluation">Order of evaluation</h3>
-
-<p>
-At package level, <a href="#Package_initialization">initialization dependencies</a>
-determine the evaluation order of individual initialization expressions in
-<a href="#Variable_declarations">variable declarations</a>.
-Otherwise, when evaluating the <a href="#Operands">operands</a> of an
-expression, assignment, or
-<a href="#Return_statements">return statement</a>,
-all function calls, method calls, and
-communication operations are evaluated in lexical left-to-right
-order.
-</p>
-
-<p>
-For example, in the (function-local) assignment
-</p>
-<pre>
-y[f()], ok = g(h(), i()+x[j()], <-c), k()
-</pre>
-<p>
-the function calls and communication happen in the order
-<code>f()</code>, <code>h()</code>, <code>i()</code>, <code>j()</code>,
-<code><-c</code>, <code>g()</code>, and <code>k()</code>.
-However, the order of those events compared to the evaluation
-and indexing of <code>x</code> and the evaluation
-of <code>y</code> is not specified.
-</p>
-
-<pre>
-a := 1
-f := func() int { a++; return a }
-x := []int{a, f()} // x may be [1, 2] or [2, 2]: evaluation order between a and f() is not specified
-m := map[int]int{a: 1, a: 2} // m may be {2: 1} or {2: 2}: evaluation order between the two map assignments is not specified
-n := map[int]int{a: f()} // n may be {2: 3} or {3: 3}: evaluation order between the key and the value is not specified
-</pre>
-
-<p>
-At package level, initialization dependencies override the left-to-right rule
-for individual initialization expressions, but not for operands within each
-expression:
-</p>
-
-<pre>
-var a, b, c = f() + v(), g(), sqr(u()) + v()
-
-func f() int { return c }
-func g() int { return a }
-func sqr(x int) int { return x*x }
-
-// functions u and v are independent of all other variables and functions
-</pre>
-
-<p>
-The function calls happen in the order
-<code>u()</code>, <code>sqr()</code>, <code>v()</code>,
-<code>f()</code>, <code>v()</code>, and <code>g()</code>.
-</p>
-
-<p>
-Floating-point operations within a single expression are evaluated according to
-the associativity of the operators. Explicit parentheses affect the evaluation
-by overriding the default associativity.
-In the expression <code>x + (y + z)</code> the addition <code>y + z</code>
-is performed before adding <code>x</code>.
-</p>
-
-<h2 id="Statements">Statements</h2>
-
-<p>
-Statements control execution.
-</p>
-
-<pre class="ebnf">
-Statement =
- Declaration | LabeledStmt | SimpleStmt |
- GoStmt | ReturnStmt | BreakStmt | ContinueStmt | GotoStmt |
- FallthroughStmt | Block | IfStmt | SwitchStmt | SelectStmt | ForStmt |
- DeferStmt .
-
-SimpleStmt = EmptyStmt | ExpressionStmt | SendStmt | IncDecStmt | Assignment | ShortVarDecl .
-</pre>
-
-<h3 id="Terminating_statements">Terminating statements</h3>
-
-<p>
-A <i>terminating statement</i> interrupts the regular flow of control in
-a <a href="#Blocks">block</a>. The following statements are terminating:
-</p>
-
-<ol>
-<li>
- A <a href="#Return_statements">"return"</a> or
- <a href="#Goto_statements">"goto"</a> statement.
- <!-- ul below only for regular layout -->
- <ul> </ul>
-</li>
-
-<li>
- A call to the built-in function
- <a href="#Handling_panics"><code>panic</code></a>.
- <!-- ul below only for regular layout -->
- <ul> </ul>
-</li>
-
-<li>
- A <a href="#Blocks">block</a> in which the statement list ends in a terminating statement.
- <!-- ul below only for regular layout -->
- <ul> </ul>
-</li>
-
-<li>
- An <a href="#If_statements">"if" statement</a> in which:
- <ul>
- <li>the "else" branch is present, and</li>
- <li>both branches are terminating statements.</li>
- </ul>
-</li>
-
-<li>
- A <a href="#For_statements">"for" statement</a> in which:
- <ul>
- <li>there are no "break" statements referring to the "for" statement, and</li>
- <li>the loop condition is absent, and</li>
- <li>the "for" statement does not use a range clause.</li>
- </ul>
-</li>
-
-<li>
- A <a href="#Switch_statements">"switch" statement</a> in which:
- <ul>
- <li>there are no "break" statements referring to the "switch" statement,</li>
- <li>there is a default case, and</li>
- <li>the statement lists in each case, including the default, end in a terminating
- statement, or a possibly labeled <a href="#Fallthrough_statements">"fallthrough"
- statement</a>.</li>
- </ul>
-</li>
-
-<li>
- A <a href="#Select_statements">"select" statement</a> in which:
- <ul>
- <li>there are no "break" statements referring to the "select" statement, and</li>
- <li>the statement lists in each case, including the default if present,
- end in a terminating statement.</li>
- </ul>
-</li>
-
-<li>
- A <a href="#Labeled_statements">labeled statement</a> labeling
- a terminating statement.
-</li>
-</ol>
-
-<p>
-All other statements are not terminating.
-</p>
-
-<p>
-A <a href="#Blocks">statement list</a> ends in a terminating statement if the list
-is not empty and its final non-empty statement is terminating.
-</p>
-
-
-<h3 id="Empty_statements">Empty statements</h3>
-
-<p>
-The empty statement does nothing.
-</p>
-
-<pre class="ebnf">
-EmptyStmt = .
-</pre>
-
-
-<h3 id="Labeled_statements">Labeled statements</h3>
-
-<p>
-A labeled statement may be the target of a <code>goto</code>,
-<code>break</code> or <code>continue</code> statement.
-</p>
-
-<pre class="ebnf">
-LabeledStmt = Label ":" Statement .
-Label = identifier .
-</pre>
-
-<pre>
-Error: log.Panic("error encountered")
-</pre>
-
-
-<h3 id="Expression_statements">Expression statements</h3>
-
-<p>
-With the exception of specific built-in functions,
-function and method <a href="#Calls">calls</a> and
-<a href="#Receive_operator">receive operations</a>
-can appear in statement context. Such statements may be parenthesized.
-</p>
-
-<pre class="ebnf">
-ExpressionStmt = Expression .
-</pre>
-
-<p>
-The following built-in functions are not permitted in statement context:
-</p>
-
-<pre>
-append cap complex imag len make new real
-unsafe.Add unsafe.Alignof unsafe.Offsetof unsafe.Sizeof unsafe.Slice
-</pre>
-
-<pre>
-h(x+y)
-f.Close()
-<-ch
-(<-ch)
-len("foo") // illegal if len is the built-in function
-</pre>
-
-
-<h3 id="Send_statements">Send statements</h3>
-
-<p>
-A send statement sends a value on a channel.
-The channel expression's <a href="#Core_types">core type</a>
-must be a <a href="#Channel_types">channel</a>,
-the channel direction must permit send operations,
-and the type of the value to be sent must be <a href="#Assignability">assignable</a>
-to the channel's element type.
-</p>
-
-<pre class="ebnf">
-SendStmt = Channel "<-" Expression .
-Channel = Expression .
-</pre>
-
-<p>
-Both the channel and the value expression are evaluated before communication
-begins. Communication blocks until the send can proceed.
-A send on an unbuffered channel can proceed if a receiver is ready.
-A send on a buffered channel can proceed if there is room in the buffer.
-A send on a closed channel proceeds by causing a <a href="#Run_time_panics">run-time panic</a>.
-A send on a <code>nil</code> channel blocks forever.
-</p>
-
-<pre>
-ch <- 3 // send value 3 to channel ch
-</pre>
-
-
-<h3 id="IncDec_statements">IncDec statements</h3>
-
-<p>
-The "++" and "--" statements increment or decrement their operands
-by the untyped <a href="#Constants">constant</a> <code>1</code>.
-As with an assignment, the operand must be <a href="#Address_operators">addressable</a>
-or a map index expression.
-</p>
-
-<pre class="ebnf">
-IncDecStmt = Expression ( "++" | "--" ) .
-</pre>
-
-<p>
-The following <a href="#Assignments">assignment statements</a> are semantically
-equivalent:
-</p>
-
-<pre class="grammar">
-IncDec statement Assignment
-x++ x += 1
-x-- x -= 1
-</pre>
-
-
-<h3 id="Assignments">Assignments</h3>
-
-<pre class="ebnf">
-Assignment = ExpressionList assign_op ExpressionList .
-
-assign_op = [ add_op | mul_op ] "=" .
-</pre>
-
-<p>
-Each left-hand side operand must be <a href="#Address_operators">addressable</a>,
-a map index expression, or (for <code>=</code> assignments only) the
-<a href="#Blank_identifier">blank identifier</a>.
-Operands may be parenthesized.
-</p>
-
-<pre>
-x = 1
-*p = f()
-a[i] = 23
-(k) = <-ch // same as: k = <-ch
-</pre>
-
-<p>
-An <i>assignment operation</i> <code>x</code> <i>op</i><code>=</code>
-<code>y</code> where <i>op</i> is a binary <a href="#Arithmetic_operators">arithmetic operator</a>
-is equivalent to <code>x</code> <code>=</code> <code>x</code> <i>op</i>
-<code>(y)</code> but evaluates <code>x</code>
-only once. The <i>op</i><code>=</code> construct is a single token.
-In assignment operations, both the left- and right-hand expression lists
-must contain exactly one single-valued expression, and the left-hand
-expression must not be the blank identifier.
-</p>
-
-<pre>
-a[i] <<= 2
-i &^= 1<<n
-</pre>
-
-<p>
-A tuple assignment assigns the individual elements of a multi-valued
-operation to a list of variables. There are two forms. In the
-first, the right hand operand is a single multi-valued expression
-such as a function call, a <a href="#Channel_types">channel</a> or
-<a href="#Map_types">map</a> operation, or a <a href="#Type_assertions">type assertion</a>.
-The number of operands on the left
-hand side must match the number of values. For instance, if
-<code>f</code> is a function returning two values,
-</p>
-
-<pre>
-x, y = f()
-</pre>
-
-<p>
-assigns the first value to <code>x</code> and the second to <code>y</code>.
-In the second form, the number of operands on the left must equal the number
-of expressions on the right, each of which must be single-valued, and the
-<i>n</i>th expression on the right is assigned to the <i>n</i>th
-operand on the left:
-</p>
-
-<pre>
-one, two, three = '一', '二', '三'
-</pre>
-
-<p>
-The <a href="#Blank_identifier">blank identifier</a> provides a way to
-ignore right-hand side values in an assignment:
-</p>
-
-<pre>
-_ = x // evaluate x but ignore it
-x, _ = f() // evaluate f() but ignore second result value
-</pre>
-
-<p>
-The assignment proceeds in two phases.
-First, the operands of <a href="#Index_expressions">index expressions</a>
-and <a href="#Address_operators">pointer indirections</a>
-(including implicit pointer indirections in <a href="#Selectors">selectors</a>)
-on the left and the expressions on the right are all
-<a href="#Order_of_evaluation">evaluated in the usual order</a>.
-Second, the assignments are carried out in left-to-right order.
-</p>
-
-<pre>
-a, b = b, a // exchange a and b
-
-x := []int{1, 2, 3}
-i := 0
-i, x[i] = 1, 2 // set i = 1, x[0] = 2
-
-i = 0
-x[i], i = 2, 1 // set x[0] = 2, i = 1
-
-x[0], x[0] = 1, 2 // set x[0] = 1, then x[0] = 2 (so x[0] == 2 at end)
-
-x[1], x[3] = 4, 5 // set x[1] = 4, then panic setting x[3] = 5.
-
-type Point struct { x, y int }
-var p *Point
-x[2], p.x = 6, 7 // set x[2] = 6, then panic setting p.x = 7
-
-i = 2
-x = []int{3, 5, 7}
-for i, x[i] = range x { // set i, x[2] = 0, x[0]
- break
-}
-// after this loop, i == 0 and x == []int{3, 5, 3}
-</pre>
-
-<p>
-In assignments, each value must be <a href="#Assignability">assignable</a>
-to the type of the operand to which it is assigned, with the following special cases:
-</p>
-
-<ol>
-<li>
- Any typed value may be assigned to the blank identifier.
-</li>
-
-<li>
- If an untyped constant
- is assigned to a variable of interface type or the blank identifier,
- the constant is first implicitly <a href="#Conversions">converted</a> to its
- <a href="#Constants">default type</a>.
-</li>
-
-<li>
- If an untyped boolean value is assigned to a variable of interface type or
- the blank identifier, it is first implicitly converted to type <code>bool</code>.
-</li>
-</ol>
-
-<h3 id="If_statements">If statements</h3>
-
-<p>
-"If" statements specify the conditional execution of two branches
-according to the value of a boolean expression. If the expression
-evaluates to true, the "if" branch is executed, otherwise, if
-present, the "else" branch is executed.
-</p>
-
-<pre class="ebnf">
-IfStmt = "if" [ SimpleStmt ";" ] Expression Block [ "else" ( IfStmt | Block ) ] .
-</pre>
-
-<pre>
-if x > max {
- x = max
-}
-</pre>
-
-<p>
-The expression may be preceded by a simple statement, which
-executes before the expression is evaluated.
-</p>
-
-<pre>
-if x := f(); x < y {
- return x
-} else if x > z {
- return z
-} else {
- return y
-}
-</pre>
-
-
-<h3 id="Switch_statements">Switch statements</h3>
-
-<p>
-"Switch" statements provide multi-way execution.
-An expression or type is compared to the "cases"
-inside the "switch" to determine which branch
-to execute.
-</p>
-
-<pre class="ebnf">
-SwitchStmt = ExprSwitchStmt | TypeSwitchStmt .
-</pre>
-
-<p>
-There are two forms: expression switches and type switches.
-In an expression switch, the cases contain expressions that are compared
-against the value of the switch expression.
-In a type switch, the cases contain types that are compared against the
-type of a specially annotated switch expression.
-The switch expression is evaluated exactly once in a switch statement.
-</p>
-
-<h4 id="Expression_switches">Expression switches</h4>
-
-<p>
-In an expression switch,
-the switch expression is evaluated and
-the case expressions, which need not be constants,
-are evaluated left-to-right and top-to-bottom; the first one that equals the
-switch expression
-triggers execution of the statements of the associated case;
-the other cases are skipped.
-If no case matches and there is a "default" case,
-its statements are executed.
-There can be at most one default case and it may appear anywhere in the
-"switch" statement.
-A missing switch expression is equivalent to the boolean value
-<code>true</code>.
-</p>
-
-<pre class="ebnf">
-ExprSwitchStmt = "switch" [ SimpleStmt ";" ] [ Expression ] "{" { ExprCaseClause } "}" .
-ExprCaseClause = ExprSwitchCase ":" StatementList .
-ExprSwitchCase = "case" ExpressionList | "default" .
-</pre>
-
-<p>
-If the switch expression evaluates to an untyped constant, it is first implicitly
-<a href="#Conversions">converted</a> to its <a href="#Constants">default type</a>.
-The predeclared untyped value <code>nil</code> cannot be used as a switch expression.
-The switch expression type must be <a href="#Comparison_operators">comparable</a>.
-</p>
-
-<p>
-If a case expression is untyped, it is first implicitly <a href="#Conversions">converted</a>
-to the type of the switch expression.
-For each (possibly converted) case expression <code>x</code> and the value <code>t</code>
-of the switch expression, <code>x == t</code> must be a valid <a href="#Comparison_operators">comparison</a>.
-</p>
-
-<p>
-In other words, the switch expression is treated as if it were used to declare and
-initialize a temporary variable <code>t</code> without explicit type; it is that
-value of <code>t</code> against which each case expression <code>x</code> is tested
-for equality.
-</p>
-
-<p>
-In a case or default clause, the last non-empty statement
-may be a (possibly <a href="#Labeled_statements">labeled</a>)
-<a href="#Fallthrough_statements">"fallthrough" statement</a> to
-indicate that control should flow from the end of this clause to
-the first statement of the next clause.
-Otherwise control flows to the end of the "switch" statement.
-A "fallthrough" statement may appear as the last statement of all
-but the last clause of an expression switch.
-</p>
-
-<p>
-The switch expression may be preceded by a simple statement, which
-executes before the expression is evaluated.
-</p>
-
-<pre>
-switch tag {
-default: s3()
-case 0, 1, 2, 3: s1()
-case 4, 5, 6, 7: s2()
-}
-
-switch x := f(); { // missing switch expression means "true"
-case x < 0: return -x
-default: return x
-}
-
-switch {
-case x < y: f1()
-case x < z: f2()
-case x == 4: f3()
-}
-</pre>
-
-<p>
-Implementation restriction: A compiler may disallow multiple case
-expressions evaluating to the same constant.
-For instance, the current compilers disallow duplicate integer,
-floating point, or string constants in case expressions.
-</p>
-
-<h4 id="Type_switches">Type switches</h4>
-
-<p>
-A type switch compares types rather than values. It is otherwise similar
-to an expression switch. It is marked by a special switch expression that
-has the form of a <a href="#Type_assertions">type assertion</a>
-using the keyword <code>type</code> rather than an actual type:
-</p>
-
-<pre>
-switch x.(type) {
-// cases
-}
-</pre>
-
-<p>
-Cases then match actual types <code>T</code> against the dynamic type of the
-expression <code>x</code>. As with type assertions, <code>x</code> must be of
-<a href="#Interface_types">interface type</a>, but not a
-<a href="#Type_parameter_declarations">type parameter</a>, and each non-interface type
-<code>T</code> listed in a case must implement the type of <code>x</code>.
-The types listed in the cases of a type switch must all be
-<a href="#Type_identity">different</a>.
-</p>
-
-<pre class="ebnf">
-TypeSwitchStmt = "switch" [ SimpleStmt ";" ] TypeSwitchGuard "{" { TypeCaseClause } "}" .
-TypeSwitchGuard = [ identifier ":=" ] PrimaryExpr "." "(" "type" ")" .
-TypeCaseClause = TypeSwitchCase ":" StatementList .
-TypeSwitchCase = "case" TypeList | "default" .
-</pre>
-
-<p>
-The TypeSwitchGuard may include a
-<a href="#Short_variable_declarations">short variable declaration</a>.
-When that form is used, the variable is declared at the end of the
-TypeSwitchCase in the <a href="#Blocks">implicit block</a> of each clause.
-In clauses with a case listing exactly one type, the variable
-has that type; otherwise, the variable has the type of the expression
-in the TypeSwitchGuard.
-</p>
-
-<p>
-Instead of a type, a case may use the predeclared identifier
-<a href="#Predeclared_identifiers"><code>nil</code></a>;
-that case is selected when the expression in the TypeSwitchGuard
-is a <code>nil</code> interface value.
-There may be at most one <code>nil</code> case.
-</p>
-
-<p>
-Given an expression <code>x</code> of type <code>interface{}</code>,
-the following type switch:
-</p>
-
-<pre>
-switch i := x.(type) {
-case nil:
- printString("x is nil") // type of i is type of x (interface{})
-case int:
- printInt(i) // type of i is int
-case float64:
- printFloat64(i) // type of i is float64
-case func(int) float64:
- printFunction(i) // type of i is func(int) float64
-case bool, string:
- printString("type is bool or string") // type of i is type of x (interface{})
-default:
- printString("don't know the type") // type of i is type of x (interface{})
-}
-</pre>
-
-<p>
-could be rewritten:
-</p>
-
-<pre>
-v := x // x is evaluated exactly once
-if v == nil {
- i := v // type of i is type of x (interface{})
- printString("x is nil")
-} else if i, isInt := v.(int); isInt {
- printInt(i) // type of i is int
-} else if i, isFloat64 := v.(float64); isFloat64 {
- printFloat64(i) // type of i is float64
-} else if i, isFunc := v.(func(int) float64); isFunc {
- printFunction(i) // type of i is func(int) float64
-} else {
- _, isBool := v.(bool)
- _, isString := v.(string)
- if isBool || isString {
- i := v // type of i is type of x (interface{})
- printString("type is bool or string")
- } else {
- i := v // type of i is type of x (interface{})
- printString("don't know the type")
- }
-}
-</pre>
-
-<p>
-A <a href="#Type_parameter_declarations">type parameter</a> or a <a href="#Type_declarations">generic type</a>
-may be used as a type in a case. If upon <a href="#Instantiations">instantiation</a> that type turns
-out to duplicate another entry in the switch, the first matching case is chosen.
-</p>
-
-<pre>
-func f[P any](x any) int {
- switch x.(type) {
- case P:
- return 0
- case string:
- return 1
- case []P:
- return 2
- case []byte:
- return 3
- default:
- return 4
- }
-}
-
-var v1 = f[string]("foo") // v1 == 0
-var v2 = f[byte]([]byte{}) // v2 == 2
-</pre>
-
-<p>
-The type switch guard may be preceded by a simple statement, which
-executes before the guard is evaluated.
-</p>
-
-<p>
-The "fallthrough" statement is not permitted in a type switch.
-</p>
-
-<h3 id="For_statements">For statements</h3>
-
-<p>
-A "for" statement specifies repeated execution of a block. There are three forms:
-The iteration may be controlled by a single condition, a "for" clause, or a "range" clause.
-</p>
-
-<pre class="ebnf">
-ForStmt = "for" [ Condition | ForClause | RangeClause ] Block .
-Condition = Expression .
-</pre>
-
-<h4 id="For_condition">For statements with single condition</h4>
-
-<p>
-In its simplest form, a "for" statement specifies the repeated execution of
-a block as long as a boolean condition evaluates to true.
-The condition is evaluated before each iteration.
-If the condition is absent, it is equivalent to the boolean value
-<code>true</code>.
-</p>
-
-<pre>
-for a < b {
- a *= 2
-}
-</pre>
-
-<h4 id="For_clause">For statements with <code>for</code> clause</h4>
-
-<p>
-A "for" statement with a ForClause is also controlled by its condition, but
-additionally it may specify an <i>init</i>
-and a <i>post</i> statement, such as an assignment,
-an increment or decrement statement. The init statement may be a
-<a href="#Short_variable_declarations">short variable declaration</a>, but the post statement must not.
-Variables declared by the init statement are re-used in each iteration.
-</p>
-
-<pre class="ebnf">
-ForClause = [ InitStmt ] ";" [ Condition ] ";" [ PostStmt ] .
-InitStmt = SimpleStmt .
-PostStmt = SimpleStmt .
-</pre>
-
-<pre>
-for i := 0; i < 10; i++ {
- f(i)
-}
-</pre>
-
-<p>
-If non-empty, the init statement is executed once before evaluating the
-condition for the first iteration;
-the post statement is executed after each execution of the block (and
-only if the block was executed).
-Any element of the ForClause may be empty but the
-<a href="#Semicolons">semicolons</a> are
-required unless there is only a condition.
-If the condition is absent, it is equivalent to the boolean value
-<code>true</code>.
-</p>
-
-<pre>
-for cond { S() } is the same as for ; cond ; { S() }
-for { S() } is the same as for true { S() }
-</pre>
-
-<h4 id="For_range">For statements with <code>range</code> clause</h4>
-
-<p>
-A "for" statement with a "range" clause
-iterates through all entries of an array, slice, string or map,
-or values received on a channel. For each entry it assigns <i>iteration values</i>
-to corresponding <i>iteration variables</i> if present and then executes the block.
-</p>
-
-<pre class="ebnf">
-RangeClause = [ ExpressionList "=" | IdentifierList ":=" ] "range" Expression .
-</pre>
-
-<p>
-The expression on the right in the "range" clause is called the <i>range expression</i>,
-its <a href="#Core_types">core type</a> must be
-an array, pointer to an array, slice, string, map, or channel permitting
-<a href="#Receive_operator">receive operations</a>.
-As with an assignment, if present the operands on the left must be
-<a href="#Address_operators">addressable</a> or map index expressions; they
-denote the iteration variables. If the range expression is a channel, at most
-one iteration variable is permitted, otherwise there may be up to two.
-If the last iteration variable is the <a href="#Blank_identifier">blank identifier</a>,
-the range clause is equivalent to the same clause without that identifier.
-</p>
-
-<p>
-The range expression <code>x</code> is evaluated once before beginning the loop,
-with one exception: if at most one iteration variable is present and
-<code>len(x)</code> is <a href="#Length_and_capacity">constant</a>,
-the range expression is not evaluated.
-</p>
-
-<p>
-Function calls on the left are evaluated once per iteration.
-For each iteration, iteration values are produced as follows
-if the respective iteration variables are present:
-</p>
-
-<pre class="grammar">
-Range expression 1st value 2nd value
-
-array or slice a [n]E, *[n]E, or []E index i int a[i] E
-string s string type index i int see below rune
-map m map[K]V key k K m[k] V
-channel c chan E, <-chan E element e E
-</pre>
-
-<ol>
-<li>
-For an array, pointer to array, or slice value <code>a</code>, the index iteration
-values are produced in increasing order, starting at element index 0.
-If at most one iteration variable is present, the range loop produces
-iteration values from 0 up to <code>len(a)-1</code> and does not index into the array
-or slice itself. For a <code>nil</code> slice, the number of iterations is 0.
-</li>
-
-<li>
-For a string value, the "range" clause iterates over the Unicode code points
-in the string starting at byte index 0. On successive iterations, the index value will be the
-index of the first byte of successive UTF-8-encoded code points in the string,
-and the second value, of type <code>rune</code>, will be the value of
-the corresponding code point. If the iteration encounters an invalid
-UTF-8 sequence, the second value will be <code>0xFFFD</code>,
-the Unicode replacement character, and the next iteration will advance
-a single byte in the string.
-</li>
-
-<li>
-The iteration order over maps is not specified
-and is not guaranteed to be the same from one iteration to the next.
-If a map entry that has not yet been reached is removed during iteration,
-the corresponding iteration value will not be produced. If a map entry is
-created during iteration, that entry may be produced during the iteration or
-may be skipped. The choice may vary for each entry created and from one
-iteration to the next.
-If the map is <code>nil</code>, the number of iterations is 0.
-</li>
-
-<li>
-For channels, the iteration values produced are the successive values sent on
-the channel until the channel is <a href="#Close">closed</a>. If the channel
-is <code>nil</code>, the range expression blocks forever.
-</li>
-</ol>
-
-<p>
-The iteration values are assigned to the respective
-iteration variables as in an <a href="#Assignments">assignment statement</a>.
-</p>
-
-<p>
-The iteration variables may be declared by the "range" clause using a form of
-<a href="#Short_variable_declarations">short variable declaration</a>
-(<code>:=</code>).
-In this case their types are set to the types of the respective iteration values
-and their <a href="#Declarations_and_scope">scope</a> is the block of the "for"
-statement; they are re-used in each iteration.
-If the iteration variables are declared outside the "for" statement,
-after execution their values will be those of the last iteration.
-</p>
-
-<pre>
-var testdata *struct {
- a *[7]int
-}
-for i, _ := range testdata.a {
- // testdata.a is never evaluated; len(testdata.a) is constant
- // i ranges from 0 to 6
- f(i)
-}
-
-var a [10]string
-for i, s := range a {
- // type of i is int
- // type of s is string
- // s == a[i]
- g(i, s)
-}
-
-var key string
-var val interface{} // element type of m is assignable to val
-m := map[string]int{"mon":0, "tue":1, "wed":2, "thu":3, "fri":4, "sat":5, "sun":6}
-for key, val = range m {
- h(key, val)
-}
-// key == last map key encountered in iteration
-// val == map[key]
-
-var ch chan Work = producer()
-for w := range ch {
- doWork(w)
-}
-
-// empty a channel
-for range ch {}
-</pre>
-
-
-<h3 id="Go_statements">Go statements</h3>
-
-<p>
-A "go" statement starts the execution of a function call
-as an independent concurrent thread of control, or <i>goroutine</i>,
-within the same address space.
-</p>
-
-<pre class="ebnf">
-GoStmt = "go" Expression .
-</pre>
-
-<p>
-The expression must be a function or method call; it cannot be parenthesized.
-Calls of built-in functions are restricted as for
-<a href="#Expression_statements">expression statements</a>.
-</p>
-
-<p>
-The function value and parameters are
-<a href="#Calls">evaluated as usual</a>
-in the calling goroutine, but
-unlike with a regular call, program execution does not wait
-for the invoked function to complete.
-Instead, the function begins executing independently
-in a new goroutine.
-When the function terminates, its goroutine also terminates.
-If the function has any return values, they are discarded when the
-function completes.
-</p>
-
-<pre>
-go Server()
-go func(ch chan<- bool) { for { sleep(10); ch <- true }} (c)
-</pre>
-
-
-<h3 id="Select_statements">Select statements</h3>
-
-<p>
-A "select" statement chooses which of a set of possible
-<a href="#Send_statements">send</a> or
-<a href="#Receive_operator">receive</a>
-operations will proceed.
-It looks similar to a
-<a href="#Switch_statements">"switch"</a> statement but with the
-cases all referring to communication operations.
-</p>
-
-<pre class="ebnf">
-SelectStmt = "select" "{" { CommClause } "}" .
-CommClause = CommCase ":" StatementList .
-CommCase = "case" ( SendStmt | RecvStmt ) | "default" .
-RecvStmt = [ ExpressionList "=" | IdentifierList ":=" ] RecvExpr .
-RecvExpr = Expression .
-</pre>
-
-<p>
-A case with a RecvStmt may assign the result of a RecvExpr to one or
-two variables, which may be declared using a
-<a href="#Short_variable_declarations">short variable declaration</a>.
-The RecvExpr must be a (possibly parenthesized) receive operation.
-There can be at most one default case and it may appear anywhere
-in the list of cases.
-</p>
-
-<p>
-Execution of a "select" statement proceeds in several steps:
-</p>
-
-<ol>
-<li>
-For all the cases in the statement, the channel operands of receive operations
-and the channel and right-hand-side expressions of send statements are
-evaluated exactly once, in source order, upon entering the "select" statement.
-The result is a set of channels to receive from or send to,
-and the corresponding values to send.
-Any side effects in that evaluation will occur irrespective of which (if any)
-communication operation is selected to proceed.
-Expressions on the left-hand side of a RecvStmt with a short variable declaration
-or assignment are not yet evaluated.
-</li>
-
-<li>
-If one or more of the communications can proceed,
-a single one that can proceed is chosen via a uniform pseudo-random selection.
-Otherwise, if there is a default case, that case is chosen.
-If there is no default case, the "select" statement blocks until
-at least one of the communications can proceed.
-</li>
-
-<li>
-Unless the selected case is the default case, the respective communication
-operation is executed.
-</li>
-
-<li>
-If the selected case is a RecvStmt with a short variable declaration or
-an assignment, the left-hand side expressions are evaluated and the
-received value (or values) are assigned.
-</li>
-
-<li>
-The statement list of the selected case is executed.
-</li>
-</ol>
-
-<p>
-Since communication on <code>nil</code> channels can never proceed,
-a select with only <code>nil</code> channels and no default case blocks forever.
-</p>
-
-<pre>
-var a []int
-var c, c1, c2, c3, c4 chan int
-var i1, i2 int
-select {
-case i1 = <-c1:
- print("received ", i1, " from c1\n")
-case c2 <- i2:
- print("sent ", i2, " to c2\n")
-case i3, ok := (<-c3): // same as: i3, ok := <-c3
- if ok {
- print("received ", i3, " from c3\n")
- } else {
- print("c3 is closed\n")
- }
-case a[f()] = <-c4:
- // same as:
- // case t := <-c4
- // a[f()] = t
-default:
- print("no communication\n")
-}
-
-for { // send random sequence of bits to c
- select {
- case c <- 0: // note: no statement, no fallthrough, no folding of cases
- case c <- 1:
- }
-}
-
-select {} // block forever
-</pre>
-
-
-<h3 id="Return_statements">Return statements</h3>
-
-<p>
-A "return" statement in a function <code>F</code> terminates the execution
-of <code>F</code>, and optionally provides one or more result values.
-Any functions <a href="#Defer_statements">deferred</a> by <code>F</code>
-are executed before <code>F</code> returns to its caller.
-</p>
-
-<pre class="ebnf">
-ReturnStmt = "return" [ ExpressionList ] .
-</pre>
-
-<p>
-In a function without a result type, a "return" statement must not
-specify any result values.
-</p>
-<pre>
-func noResult() {
- return
-}
-</pre>
-
-<p>
-There are three ways to return values from a function with a result
-type:
-</p>
-
-<ol>
- <li>The return value or values may be explicitly listed
- in the "return" statement. Each expression must be single-valued
- and <a href="#Assignability">assignable</a>
- to the corresponding element of the function's result type.
-<pre>
-func simpleF() int {
- return 2
-}
-
-func complexF1() (re float64, im float64) {
- return -7.0, -4.0
-}
-</pre>
- </li>
- <li>The expression list in the "return" statement may be a single
- call to a multi-valued function. The effect is as if each value
- returned from that function were assigned to a temporary
- variable with the type of the respective value, followed by a
- "return" statement listing these variables, at which point the
- rules of the previous case apply.
-<pre>
-func complexF2() (re float64, im float64) {
- return complexF1()
-}
-</pre>
- </li>
- <li>The expression list may be empty if the function's result
- type specifies names for its <a href="#Function_types">result parameters</a>.
- The result parameters act as ordinary local variables
- and the function may assign values to them as necessary.
- The "return" statement returns the values of these variables.
-<pre>
-func complexF3() (re float64, im float64) {
- re = 7.0
- im = 4.0
- return
-}
-
-func (devnull) Write(p []byte) (n int, _ error) {
- n = len(p)
- return
-}
-</pre>
- </li>
-</ol>
-
-<p>
-Regardless of how they are declared, all the result values are initialized to
-the <a href="#The_zero_value">zero values</a> for their type upon entry to the
-function. A "return" statement that specifies results sets the result parameters before
-any deferred functions are executed.
-</p>
-
-<p>
-Implementation restriction: A compiler may disallow an empty expression list
-in a "return" statement if a different entity (constant, type, or variable)
-with the same name as a result parameter is in
-<a href="#Declarations_and_scope">scope</a> at the place of the return.
-</p>
-
-<pre>
-func f(n int) (res int, err error) {
- if _, err := f(n-1); err != nil {
- return // invalid return statement: err is shadowed
- }
- return
-}
-</pre>
-
-<h3 id="Break_statements">Break statements</h3>
-
-<p>
-A "break" statement terminates execution of the innermost
-<a href="#For_statements">"for"</a>,
-<a href="#Switch_statements">"switch"</a>, or
-<a href="#Select_statements">"select"</a> statement
-within the same function.
-</p>
-
-<pre class="ebnf">
-BreakStmt = "break" [ Label ] .
-</pre>
-
-<p>
-If there is a label, it must be that of an enclosing
-"for", "switch", or "select" statement,
-and that is the one whose execution terminates.
-</p>
-
-<pre>
-OuterLoop:
- for i = 0; i < n; i++ {
- for j = 0; j < m; j++ {
- switch a[i][j] {
- case nil:
- state = Error
- break OuterLoop
- case item:
- state = Found
- break OuterLoop
- }
- }
- }
-</pre>
-
-<h3 id="Continue_statements">Continue statements</h3>
-
-<p>
-A "continue" statement begins the next iteration of the
-innermost <a href="#For_statements">"for" loop</a> at its post statement.
-The "for" loop must be within the same function.
-</p>
-
-<pre class="ebnf">
-ContinueStmt = "continue" [ Label ] .
-</pre>
-
-<p>
-If there is a label, it must be that of an enclosing
-"for" statement, and that is the one whose execution
-advances.
-</p>
-
-<pre>
-RowLoop:
- for y, row := range rows {
- for x, data := range row {
- if data == endOfRow {
- continue RowLoop
- }
- row[x] = data + bias(x, y)
- }
- }
-</pre>
-
-<h3 id="Goto_statements">Goto statements</h3>
-
-<p>
-A "goto" statement transfers control to the statement with the corresponding label
-within the same function.
-</p>
-
-<pre class="ebnf">
-GotoStmt = "goto" Label .
-</pre>
-
-<pre>
-goto Error
-</pre>
-
-<p>
-Executing the "goto" statement must not cause any variables to come into
-<a href="#Declarations_and_scope">scope</a> that were not already in scope at the point of the goto.
-For instance, this example:
-</p>
-
-<pre>
- goto L // BAD
- v := 3
-L:
-</pre>
-
-<p>
-is erroneous because the jump to label <code>L</code> skips
-the creation of <code>v</code>.
-</p>
-
-<p>
-A "goto" statement outside a <a href="#Blocks">block</a> cannot jump to a label inside that block.
-For instance, this example:
-</p>
-
-<pre>
-if n%2 == 1 {
- goto L1
-}
-for n > 0 {
- f()
- n--
-L1:
- f()
- n--
-}
-</pre>
-
-<p>
-is erroneous because the label <code>L1</code> is inside
-the "for" statement's block but the <code>goto</code> is not.
-</p>
-
-<h3 id="Fallthrough_statements">Fallthrough statements</h3>
-
-<p>
-A "fallthrough" statement transfers control to the first statement of the
-next case clause in an <a href="#Expression_switches">expression "switch" statement</a>.
-It may be used only as the final non-empty statement in such a clause.
-</p>
-
-<pre class="ebnf">
-FallthroughStmt = "fallthrough" .
-</pre>
-
-
-<h3 id="Defer_statements">Defer statements</h3>
-
-<p>
-A "defer" statement invokes a function whose execution is deferred
-to the moment the surrounding function returns, either because the
-surrounding function executed a <a href="#Return_statements">return statement</a>,
-reached the end of its <a href="#Function_declarations">function body</a>,
-or because the corresponding goroutine is <a href="#Handling_panics">panicking</a>.
-</p>
-
-<pre class="ebnf">
-DeferStmt = "defer" Expression .
-</pre>
-
-<p>
-The expression must be a function or method call; it cannot be parenthesized.
-Calls of built-in functions are restricted as for
-<a href="#Expression_statements">expression statements</a>.
-</p>
-
-<p>
-Each time a "defer" statement
-executes, the function value and parameters to the call are
-<a href="#Calls">evaluated as usual</a>
-and saved anew but the actual function is not invoked.
-Instead, deferred functions are invoked immediately before
-the surrounding function returns, in the reverse order
-they were deferred. That is, if the surrounding function
-returns through an explicit <a href="#Return_statements">return statement</a>,
-deferred functions are executed <i>after</i> any result parameters are set
-by that return statement but <i>before</i> the function returns to its caller.
-If a deferred function value evaluates
-to <code>nil</code>, execution <a href="#Handling_panics">panics</a>
-when the function is invoked, not when the "defer" statement is executed.
-</p>
-
-<p>
-For instance, if the deferred function is
-a <a href="#Function_literals">function literal</a> and the surrounding
-function has <a href="#Function_types">named result parameters</a> that
-are in scope within the literal, the deferred function may access and modify
-the result parameters before they are returned.
-If the deferred function has any return values, they are discarded when
-the function completes.
-(See also the section on <a href="#Handling_panics">handling panics</a>.)
-</p>
-
-<pre>
-lock(l)
-defer unlock(l) // unlocking happens before surrounding function returns
-
-// prints 3 2 1 0 before surrounding function returns
-for i := 0; i <= 3; i++ {
- defer fmt.Print(i)
-}
-
-// f returns 42
-func f() (result int) {
- defer func() {
- // result is accessed after it was set to 6 by the return statement
- result *= 7
- }()
- return 6
-}
-</pre>
-
-<h2 id="Built-in_functions">Built-in functions</h2>
-
-<p>
-Built-in functions are
-<a href="#Predeclared_identifiers">predeclared</a>.
-They are called like any other function but some of them
-accept a type instead of an expression as the first argument.
-</p>
-
-<p>
-The built-in functions do not have standard Go types,
-so they can only appear in <a href="#Calls">call expressions</a>;
-they cannot be used as function values.
-</p>
-
-<h3 id="Close">Close</h3>
-
-<p>
-For an argument <code>ch</code> with a <a href="#Core_types">core type</a>
-that is a <a href="#Channel_types">channel</a>, the built-in function <code>close</code>
-records that no more values will be sent on the channel.
-It is an error if <code>ch</code> is a receive-only channel.
-Sending to or closing a closed channel causes a <a href="#Run_time_panics">run-time panic</a>.
-Closing the nil channel also causes a <a href="#Run_time_panics">run-time panic</a>.
-After calling <code>close</code>, and after any previously
-sent values have been received, receive operations will return
-the zero value for the channel's type without blocking.
-The multi-valued <a href="#Receive_operator">receive operation</a>
-returns a received value along with an indication of whether the channel is closed.
-</p>
-
-<h3 id="Length_and_capacity">Length and capacity</h3>
-
-<p>
-The built-in functions <code>len</code> and <code>cap</code> take arguments
-of various types and return a result of type <code>int</code>.
-The implementation guarantees that the result always fits into an <code>int</code>.
-</p>
-
-<pre class="grammar">
-Call Argument type Result
-
-len(s) string type string length in bytes
- [n]T, *[n]T array length (== n)
- []T slice length
- map[K]T map length (number of defined keys)
- chan T number of elements queued in channel buffer
- type parameter see below
-
-cap(s) [n]T, *[n]T array length (== n)
- []T slice capacity
- chan T channel buffer capacity
- type parameter see below
-</pre>
-
-<p>
-If the argument type is a <a href="#Type_parameter_declarations">type parameter</a> <code>P</code>,
-the call <code>len(e)</code> (or <code>cap(e)</code> respectively) must be valid for
-each type in <code>P</code>'s type set.
-The result is the length (or capacity, respectively) of the argument whose type
-corresponds to the type argument with which <code>P</code> was
-<a href="#Instantiations">instantiated</a>.
-</p>
-
-<p>
-The capacity of a slice is the number of elements for which there is
-space allocated in the underlying array.
-At any time the following relationship holds:
-</p>
-
-<pre>
-0 <= len(s) <= cap(s)
-</pre>
-
-<p>
-The length of a <code>nil</code> slice, map or channel is 0.
-The capacity of a <code>nil</code> slice or channel is 0.
-</p>
-
-<p>
-The expression <code>len(s)</code> is <a href="#Constants">constant</a> if
-<code>s</code> is a string constant. The expressions <code>len(s)</code> and
-<code>cap(s)</code> are constants if the type of <code>s</code> is an array
-or pointer to an array and the expression <code>s</code> does not contain
-<a href="#Receive_operator">channel receives</a> or (non-constant)
-<a href="#Calls">function calls</a>; in this case <code>s</code> is not evaluated.
-Otherwise, invocations of <code>len</code> and <code>cap</code> are not
-constant and <code>s</code> is evaluated.
-</p>
-
-<pre>
-const (
- c1 = imag(2i) // imag(2i) = 2.0 is a constant
- c2 = len([10]float64{2}) // [10]float64{2} contains no function calls
- c3 = len([10]float64{c1}) // [10]float64{c1} contains no function calls
- c4 = len([10]float64{imag(2i)}) // imag(2i) is a constant and no function call is issued
- c5 = len([10]float64{imag(z)}) // invalid: imag(z) is a (non-constant) function call
-)
-var z complex128
-</pre>
-
-<h3 id="Allocation">Allocation</h3>
-
-<p>
-The built-in function <code>new</code> takes a type <code>T</code>,
-allocates storage for a <a href="#Variables">variable</a> of that type
-at run time, and returns a value of type <code>*T</code>
-<a href="#Pointer_types">pointing</a> to it.
-The variable is initialized as described in the section on
-<a href="#The_zero_value">initial values</a>.
-</p>
-
-<pre class="grammar">
-new(T)
-</pre>
-
-<p>
-For instance
-</p>
-
-<pre>
-type S struct { a int; b float64 }
-new(S)
-</pre>
-
-<p>
-allocates storage for a variable of type <code>S</code>,
-initializes it (<code>a=0</code>, <code>b=0.0</code>),
-and returns a value of type <code>*S</code> containing the address
-of the location.
-</p>
-
-<h3 id="Making_slices_maps_and_channels">Making slices, maps and channels</h3>
-
-<p>
-The built-in function <code>make</code> takes a type <code>T</code>,
-optionally followed by a type-specific list of expressions.
-The <a href="#Core_types">core type</a> of <code>T</code> must
-be a slice, map or channel.
-It returns a value of type <code>T</code> (not <code>*T</code>).
-The memory is initialized as described in the section on
-<a href="#The_zero_value">initial values</a>.
-</p>
-
-<pre class="grammar">
-Call Core type Result
-
-make(T, n) slice slice of type T with length n and capacity n
-make(T, n, m) slice slice of type T with length n and capacity m
-
-make(T) map map of type T
-make(T, n) map map of type T with initial space for approximately n elements
-
-make(T) channel unbuffered channel of type T
-make(T, n) channel buffered channel of type T, buffer size n
-</pre>
-
-
-<p>
-Each of the size arguments <code>n</code> and <code>m</code> must be of <a href="#Numeric_types">integer type</a>,
-have a <a href="#Interface_types">type set</a> containing only integer types,
-or be an untyped <a href="#Constants">constant</a>.
-A constant size argument must be non-negative and <a href="#Representability">representable</a>
-by a value of type <code>int</code>; if it is an untyped constant it is given type <code>int</code>.
-If both <code>n</code> and <code>m</code> are provided and are constant, then
-<code>n</code> must be no larger than <code>m</code>.
-If <code>n</code> is negative or larger than <code>m</code> at run time,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<pre>
-s := make([]int, 10, 100) // slice with len(s) == 10, cap(s) == 100
-s := make([]int, 1e3) // slice with len(s) == cap(s) == 1000
-s := make([]int, 1<<63) // illegal: len(s) is not representable by a value of type int
-s := make([]int, 10, 0) // illegal: len(s) > cap(s)
-c := make(chan int, 10) // channel with a buffer size of 10
-m := make(map[string]int, 100) // map with initial space for approximately 100 elements
-</pre>
-
-<p>
-Calling <code>make</code> with a map type and size hint <code>n</code> will
-create a map with initial space to hold <code>n</code> map elements.
-The precise behavior is implementation-dependent.
-</p>
-
-
-<h3 id="Appending_and_copying_slices">Appending to and copying slices</h3>
-
-<p>
-The built-in functions <code>append</code> and <code>copy</code> assist in
-common slice operations.
-For both functions, the result is independent of whether the memory referenced
-by the arguments overlaps.
-</p>
-
-<p>
-The <a href="#Function_types">variadic</a> function <code>append</code>
-appends zero or more values <code>x</code> to a slice <code>s</code>
-and returns the resulting slice of the same type as <code>s</code>.
-The <a href="#Core_types">core type</a> of <code>s</code> must be a slice
-of type <code>[]E</code>.
-The values <code>x</code> are passed to a parameter of type <code>...E</code>
-and the respective <a href="#Passing_arguments_to_..._parameters">parameter
-passing rules</a> apply.
-As a special case, if the core type of <code>s</code> is <code>[]byte</code>,
-<code>append</code> also accepts a second argument with core type <code>string</code>
-followed by <code>...</code>. This form appends the bytes of the string.
-</p>
-
-<pre class="grammar">
-append(s S, x ...E) S // core type of S is []E
-</pre>
-
-<p>
-If the capacity of <code>s</code> is not large enough to fit the additional
-values, <code>append</code> allocates a new, sufficiently large underlying
-array that fits both the existing slice elements and the additional values.
-Otherwise, <code>append</code> re-uses the underlying array.
-</p>
-
-<pre>
-s0 := []int{0, 0}
-s1 := append(s0, 2) // append a single element s1 == []int{0, 0, 2}
-s2 := append(s1, 3, 5, 7) // append multiple elements s2 == []int{0, 0, 2, 3, 5, 7}
-s3 := append(s2, s0...) // append a slice s3 == []int{0, 0, 2, 3, 5, 7, 0, 0}
-s4 := append(s3[3:6], s3[2:]...) // append overlapping slice s4 == []int{3, 5, 7, 2, 3, 5, 7, 0, 0}
-
-var t []interface{}
-t = append(t, 42, 3.1415, "foo") // t == []interface{}{42, 3.1415, "foo"}
-
-var b []byte
-b = append(b, "bar"...) // append string contents b == []byte{'b', 'a', 'r' }
-</pre>
-
-<p>
-The function <code>copy</code> copies slice elements from
-a source <code>src</code> to a destination <code>dst</code> and returns the
-number of elements copied.
-The <a href="#Core_types">core types</a> of both arguments must be slices
-with <a href="#Type_identity">identical</a> element type.
-The number of elements copied is the minimum of
-<code>len(src)</code> and <code>len(dst)</code>.
-As a special case, if the destination's core type is <code>[]byte</code>,
-<code>copy</code> also accepts a source argument with core type <code>string</code>.
-This form copies the bytes from the string into the byte slice.
-</p>
-
-<pre class="grammar">
-copy(dst, src []T) int
-copy(dst []byte, src string) int
-</pre>
-
-<p>
-Examples:
-</p>
-
-<pre>
-var a = [...]int{0, 1, 2, 3, 4, 5, 6, 7}
-var s = make([]int, 6)
-var b = make([]byte, 5)
-n1 := copy(s, a[0:]) // n1 == 6, s == []int{0, 1, 2, 3, 4, 5}
-n2 := copy(s, s[2:]) // n2 == 4, s == []int{2, 3, 4, 5, 4, 5}
-n3 := copy(b, "Hello, World!") // n3 == 5, b == []byte("Hello")
-</pre>
-
-
-<h3 id="Deletion_of_map_elements">Deletion of map elements</h3>
-
-<p>
-The built-in function <code>delete</code> removes the element with key
-<code>k</code> from a <a href="#Map_types">map</a> <code>m</code>. The
-value <code>k</code> must be <a href="#Assignability">assignable</a>
-to the key type of <code>m</code>.
-</p>
-
-<pre class="grammar">
-delete(m, k) // remove element m[k] from map m
-</pre>
-
-<p>
-If the type of <code>m</code> is a <a href="#Type_parameter_declarations">type parameter</a>,
-all types in that type set must be maps, and they must all have identical key types.
-</p>
-
-<p>
-If the map <code>m</code> is <code>nil</code> or the element <code>m[k]</code>
-does not exist, <code>delete</code> is a no-op.
-</p>
-
-
-<h3 id="Complex_numbers">Manipulating complex numbers</h3>
-
-<p>
-Three functions assemble and disassemble complex numbers.
-The built-in function <code>complex</code> constructs a complex
-value from a floating-point real and imaginary part, while
-<code>real</code> and <code>imag</code>
-extract the real and imaginary parts of a complex value.
-</p>
-
-<pre class="grammar">
-complex(realPart, imaginaryPart floatT) complexT
-real(complexT) floatT
-imag(complexT) floatT
-</pre>
-
-<p>
-The type of the arguments and return value correspond.
-For <code>complex</code>, the two arguments must be of the same
-<a href="#Numeric_types">floating-point type</a> and the return type is the
-<a href="#Numeric_types">complex type</a>
-with the corresponding floating-point constituents:
-<code>complex64</code> for <code>float32</code> arguments, and
-<code>complex128</code> for <code>float64</code> arguments.
-If one of the arguments evaluates to an untyped constant, it is first implicitly
-<a href="#Conversions">converted</a> to the type of the other argument.
-If both arguments evaluate to untyped constants, they must be non-complex
-numbers or their imaginary parts must be zero, and the return value of
-the function is an untyped complex constant.
-</p>
-
-<p>
-For <code>real</code> and <code>imag</code>, the argument must be
-of complex type, and the return type is the corresponding floating-point
-type: <code>float32</code> for a <code>complex64</code> argument, and
-<code>float64</code> for a <code>complex128</code> argument.
-If the argument evaluates to an untyped constant, it must be a number,
-and the return value of the function is an untyped floating-point constant.
-</p>
-
-<p>
-The <code>real</code> and <code>imag</code> functions together form the inverse of
-<code>complex</code>, so for a value <code>z</code> of a complex type <code>Z</code>,
-<code>z == Z(complex(real(z), imag(z)))</code>.
-</p>
-
-<p>
-If the operands of these functions are all constants, the return
-value is a constant.
-</p>
-
-<pre>
-var a = complex(2, -2) // complex128
-const b = complex(1.0, -1.4) // untyped complex constant 1 - 1.4i
-x := float32(math.Cos(math.Pi/2)) // float32
-var c64 = complex(5, -x) // complex64
-var s int = complex(1, 0) // untyped complex constant 1 + 0i can be converted to int
-_ = complex(1, 2<<s) // illegal: 2 assumes floating-point type, cannot shift
-var rl = real(c64) // float32
-var im = imag(a) // float64
-const c = imag(b) // untyped constant -1.4
-_ = imag(3 << s) // illegal: 3 assumes complex type, cannot shift
-</pre>
-
-<p>
-Arguments of type parameter type are not permitted.
-</p>
-
-<h3 id="Handling_panics">Handling panics</h3>
-
-<p> Two built-in functions, <code>panic</code> and <code>recover</code>,
-assist in reporting and handling <a href="#Run_time_panics">run-time panics</a>
-and program-defined error conditions.
-</p>
-
-<pre class="grammar">
-func panic(interface{})
-func recover() interface{}
-</pre>
-
-<p>
-While executing a function <code>F</code>,
-an explicit call to <code>panic</code> or a <a href="#Run_time_panics">run-time panic</a>
-terminates the execution of <code>F</code>.
-Any functions <a href="#Defer_statements">deferred</a> by <code>F</code>
-are then executed as usual.
-Next, any deferred functions run by <code>F</code>'s caller are run,
-and so on up to any deferred by the top-level function in the executing goroutine.
-At that point, the program is terminated and the error
-condition is reported, including the value of the argument to <code>panic</code>.
-This termination sequence is called <i>panicking</i>.
-</p>
-
-<pre>
-panic(42)
-panic("unreachable")
-panic(Error("cannot parse"))
-</pre>
-
-<p>
-The <code>recover</code> function allows a program to manage behavior
-of a panicking goroutine.
-Suppose a function <code>G</code> defers a function <code>D</code> that calls
-<code>recover</code> and a panic occurs in a function on the same goroutine in which <code>G</code>
-is executing.
-When the running of deferred functions reaches <code>D</code>,
-the return value of <code>D</code>'s call to <code>recover</code> will be the value passed to the call of <code>panic</code>.
-If <code>D</code> returns normally, without starting a new
-<code>panic</code>, the panicking sequence stops. In that case,
-the state of functions called between <code>G</code> and the call to <code>panic</code>
-is discarded, and normal execution resumes.
-Any functions deferred by <code>G</code> before <code>D</code> are then run and <code>G</code>'s
-execution terminates by returning to its caller.
-</p>
-
-<p>
-The return value of <code>recover</code> is <code>nil</code> if any of the following conditions holds:
-</p>
-<ul>
-<li>
-<code>panic</code>'s argument was <code>nil</code>;
-</li>
-<li>
-the goroutine is not panicking;
-</li>
-<li>
-<code>recover</code> was not called directly by a deferred function.
-</li>
-</ul>
-
-<p>
-The <code>protect</code> function in the example below invokes
-the function argument <code>g</code> and protects callers from
-run-time panics raised by <code>g</code>.
-</p>
-
-<pre>
-func protect(g func()) {
- defer func() {
- log.Println("done") // Println executes normally even if there is a panic
- if x := recover(); x != nil {
- log.Printf("run time panic: %v", x)
- }
- }()
- log.Println("start")
- g()
-}
-</pre>
-
-
-<h3 id="Bootstrapping">Bootstrapping</h3>
-
-<p>
-Current implementations provide several built-in functions useful during
-bootstrapping. These functions are documented for completeness but are not
-guaranteed to stay in the language. They do not return a result.
-</p>
-
-<pre class="grammar">
-Function Behavior
-
-print prints all arguments; formatting of arguments is implementation-specific
-println like print but prints spaces between arguments and a newline at the end
-</pre>
-
-<p>
-Implementation restriction: <code>print</code> and <code>println</code> need not
-accept arbitrary argument types, but printing of boolean, numeric, and string
-<a href="#Types">types</a> must be supported.
-</p>
-
-<h2 id="Packages">Packages</h2>
-
-<p>
-Go programs are constructed by linking together <i>packages</i>.
-A package in turn is constructed from one or more source files
-that together declare constants, types, variables and functions
-belonging to the package and which are accessible in all files
-of the same package. Those elements may be
-<a href="#Exported_identifiers">exported</a> and used in another package.
-</p>
-
-<h3 id="Source_file_organization">Source file organization</h3>
-
-<p>
-Each source file consists of a package clause defining the package
-to which it belongs, followed by a possibly empty set of import
-declarations that declare packages whose contents it wishes to use,
-followed by a possibly empty set of declarations of functions,
-types, variables, and constants.
-</p>
-
-<pre class="ebnf">
-SourceFile = PackageClause ";" { ImportDecl ";" } { TopLevelDecl ";" } .
-</pre>
-
-<h3 id="Package_clause">Package clause</h3>
-
-<p>
-A package clause begins each source file and defines the package
-to which the file belongs.
-</p>
-
-<pre class="ebnf">
-PackageClause = "package" PackageName .
-PackageName = identifier .
-</pre>
-
-<p>
-The PackageName must not be the <a href="#Blank_identifier">blank identifier</a>.
-</p>
-
-<pre>
-package math
-</pre>
-
-<p>
-A set of files sharing the same PackageName form the implementation of a package.
-An implementation may require that all source files for a package inhabit the same directory.
-</p>
-
-<h3 id="Import_declarations">Import declarations</h3>
-
-<p>
-An import declaration states that the source file containing the declaration
-depends on functionality of the <i>imported</i> package
-(<a href="#Program_initialization_and_execution">§Program initialization and execution</a>)
-and enables access to <a href="#Exported_identifiers">exported</a> identifiers
-of that package.
-The import names an identifier (PackageName) to be used for access and an ImportPath
-that specifies the package to be imported.
-</p>
-
-<pre class="ebnf">
-ImportDecl = "import" ( ImportSpec | "(" { ImportSpec ";" } ")" ) .
-ImportSpec = [ "." | PackageName ] ImportPath .
-ImportPath = string_lit .
-</pre>
-
-<p>
-The PackageName is used in <a href="#Qualified_identifiers">qualified identifiers</a>
-to access exported identifiers of the package within the importing source file.
-It is declared in the <a href="#Blocks">file block</a>.
-If the PackageName is omitted, it defaults to the identifier specified in the
-<a href="#Package_clause">package clause</a> of the imported package.
-If an explicit period (<code>.</code>) appears instead of a name, all the
-package's exported identifiers declared in that package's
-<a href="#Blocks">package block</a> will be declared in the importing source
-file's file block and must be accessed without a qualifier.
-</p>
-
-<p>
-The interpretation of the ImportPath is implementation-dependent but
-it is typically a substring of the full file name of the compiled
-package and may be relative to a repository of installed packages.
-</p>
-
-<p>
-Implementation restriction: A compiler may restrict ImportPaths to
-non-empty strings using only characters belonging to
-<a href="https://www.unicode.org/versions/Unicode6.3.0/">Unicode's</a>
-L, M, N, P, and S general categories (the Graphic characters without
-spaces) and may also exclude the characters
-<code>!"#$%&'()*,:;<=>?[\]^`{|}</code>
-and the Unicode replacement character U+FFFD.
-</p>
-
-<p>
-Assume we have compiled a package containing the package clause
-<code>package math</code>, which exports function <code>Sin</code>, and
-installed the compiled package in the file identified by
-<code>"lib/math"</code>.
-This table illustrates how <code>Sin</code> is accessed in files
-that import the package after the
-various types of import declaration.
-</p>
-
-<pre class="grammar">
-Import declaration Local name of Sin
-
-import "lib/math" math.Sin
-import m "lib/math" m.Sin
-import . "lib/math" Sin
-</pre>
-
-<p>
-An import declaration declares a dependency relation between
-the importing and imported package.
-It is illegal for a package to import itself, directly or indirectly,
-or to directly import a package without
-referring to any of its exported identifiers. To import a package solely for
-its side-effects (initialization), use the <a href="#Blank_identifier">blank</a>
-identifier as explicit package name:
-</p>
-
-<pre>
-import _ "lib/math"
-</pre>
-
-
-<h3 id="An_example_package">An example package</h3>
-
-<p>
-Here is a complete Go package that implements a concurrent prime sieve.
-</p>
-
-<pre>
-package main
-
-import "fmt"
-
-// Send the sequence 2, 3, 4, … to channel 'ch'.
-func generate(ch chan<- int) {
- for i := 2; ; i++ {
- ch <- i // Send 'i' to channel 'ch'.
- }
-}
-
-// Copy the values from channel 'src' to channel 'dst',
-// removing those divisible by 'prime'.
-func filter(src <-chan int, dst chan<- int, prime int) {
- for i := range src { // Loop over values received from 'src'.
- if i%prime != 0 {
- dst <- i // Send 'i' to channel 'dst'.
- }
- }
-}
-
-// The prime sieve: Daisy-chain filter processes together.
-func sieve() {
- ch := make(chan int) // Create a new channel.
- go generate(ch) // Start generate() as a subprocess.
- for {
- prime := <-ch
- fmt.Print(prime, "\n")
- ch1 := make(chan int)
- go filter(ch, ch1, prime)
- ch = ch1
- }
-}
-
-func main() {
- sieve()
-}
-</pre>
-
-<h2 id="Program_initialization_and_execution">Program initialization and execution</h2>
-
-<h3 id="The_zero_value">The zero value</h3>
-<p>
-When storage is allocated for a <a href="#Variables">variable</a>,
-either through a declaration or a call of <code>new</code>, or when
-a new value is created, either through a composite literal or a call
-of <code>make</code>,
-and no explicit initialization is provided, the variable or value is
-given a default value. Each element of such a variable or value is
-set to the <i>zero value</i> for its type: <code>false</code> for booleans,
-<code>0</code> for numeric types, <code>""</code>
-for strings, and <code>nil</code> for pointers, functions, interfaces, slices, channels, and maps.
-This initialization is done recursively, so for instance each element of an
-array of structs will have its fields zeroed if no value is specified.
-</p>
-<p>
-These two simple declarations are equivalent:
-</p>
-
-<pre>
-var i int
-var i int = 0
-</pre>
-
-<p>
-After
-</p>
-
-<pre>
-type T struct { i int; f float64; next *T }
-t := new(T)
-</pre>
-
-<p>
-the following holds:
-</p>
-
-<pre>
-t.i == 0
-t.f == 0.0
-t.next == nil
-</pre>
-
-<p>
-The same would also be true after
-</p>
-
-<pre>
-var t T
-</pre>
-
-<h3 id="Package_initialization">Package initialization</h3>
-
-<p>
-Within a package, package-level variable initialization proceeds stepwise,
-with each step selecting the variable earliest in <i>declaration order</i>
-which has no dependencies on uninitialized variables.
-</p>
-
-<p>
-More precisely, a package-level variable is considered <i>ready for
-initialization</i> if it is not yet initialized and either has
-no <a href="#Variable_declarations">initialization expression</a> or
-its initialization expression has no <i>dependencies</i> on uninitialized variables.
-Initialization proceeds by repeatedly initializing the next package-level
-variable that is earliest in declaration order and ready for initialization,
-until there are no variables ready for initialization.
-</p>
-
-<p>
-If any variables are still uninitialized when this
-process ends, those variables are part of one or more initialization cycles,
-and the program is not valid.
-</p>
-
-<p>
-Multiple variables on the left-hand side of a variable declaration initialized
-by single (multi-valued) expression on the right-hand side are initialized
-together: If any of the variables on the left-hand side is initialized, all
-those variables are initialized in the same step.
-</p>
-
-<pre>
-var x = a
-var a, b = f() // a and b are initialized together, before x is initialized
-</pre>
-
-<p>
-For the purpose of package initialization, <a href="#Blank_identifier">blank</a>
-variables are treated like any other variables in declarations.
-</p>
-
-<p>
-The declaration order of variables declared in multiple files is determined
-by the order in which the files are presented to the compiler: Variables
-declared in the first file are declared before any of the variables declared
-in the second file, and so on.
-</p>
-
-<p>
-Dependency analysis does not rely on the actual values of the
-variables, only on lexical <i>references</i> to them in the source,
-analyzed transitively. For instance, if a variable <code>x</code>'s
-initialization expression refers to a function whose body refers to
-variable <code>y</code> then <code>x</code> depends on <code>y</code>.
-Specifically:
-</p>
-
-<ul>
-<li>
-A reference to a variable or function is an identifier denoting that
-variable or function.
-</li>
-
-<li>
-A reference to a method <code>m</code> is a
-<a href="#Method_values">method value</a> or
-<a href="#Method_expressions">method expression</a> of the form
-<code>t.m</code>, where the (static) type of <code>t</code> is
-not an interface type, and the method <code>m</code> is in the
-<a href="#Method_sets">method set</a> of <code>t</code>.
-It is immaterial whether the resulting function value
-<code>t.m</code> is invoked.
-</li>
-
-<li>
-A variable, function, or method <code>x</code> depends on a variable
-<code>y</code> if <code>x</code>'s initialization expression or body
-(for functions and methods) contains a reference to <code>y</code>
-or to a function or method that depends on <code>y</code>.
-</li>
-</ul>
-
-<p>
-For example, given the declarations
-</p>
-
-<pre>
-var (
- a = c + b // == 9
- b = f() // == 4
- c = f() // == 5
- d = 3 // == 5 after initialization has finished
-)
-
-func f() int {
- d++
- return d
-}
-</pre>
-
-<p>
-the initialization order is <code>d</code>, <code>b</code>, <code>c</code>, <code>a</code>.
-Note that the order of subexpressions in initialization expressions is irrelevant:
-<code>a = c + b</code> and <code>a = b + c</code> result in the same initialization
-order in this example.
-</p>
-
-<p>
-Dependency analysis is performed per package; only references referring
-to variables, functions, and (non-interface) methods declared in the current
-package are considered. If other, hidden, data dependencies exists between
-variables, the initialization order between those variables is unspecified.
-</p>
-
-<p>
-For instance, given the declarations
-</p>
-
-<pre>
-var x = I(T{}).ab() // x has an undetected, hidden dependency on a and b
-var _ = sideEffect() // unrelated to x, a, or b
-var a = b
-var b = 42
-
-type I interface { ab() []int }
-type T struct{}
-func (T) ab() []int { return []int{a, b} }
-</pre>
-
-<p>
-the variable <code>a</code> will be initialized after <code>b</code> but
-whether <code>x</code> is initialized before <code>b</code>, between
-<code>b</code> and <code>a</code>, or after <code>a</code>, and
-thus also the moment at which <code>sideEffect()</code> is called (before
-or after <code>x</code> is initialized) is not specified.
-</p>
-
-<p>
-Variables may also be initialized using functions named <code>init</code>
-declared in the package block, with no arguments and no result parameters.
-</p>
-
-<pre>
-func init() { … }
-</pre>
-
-<p>
-Multiple such functions may be defined per package, even within a single
-source file. In the package block, the <code>init</code> identifier can
-be used only to declare <code>init</code> functions, yet the identifier
-itself is not <a href="#Declarations_and_scope">declared</a>. Thus
-<code>init</code> functions cannot be referred to from anywhere
-in a program.
-</p>
-
-<p>
-A package with no imports is initialized by assigning initial values
-to all its package-level variables followed by calling all <code>init</code>
-functions in the order they appear in the source, possibly in multiple files,
-as presented to the compiler.
-If a package has imports, the imported packages are initialized
-before initializing the package itself. If multiple packages import
-a package, the imported package will be initialized only once.
-The importing of packages, by construction, guarantees that there
-can be no cyclic initialization dependencies.
-</p>
-
-<p>
-Package initialization—variable initialization and the invocation of
-<code>init</code> functions—happens in a single goroutine,
-sequentially, one package at a time.
-An <code>init</code> function may launch other goroutines, which can run
-concurrently with the initialization code. However, initialization
-always sequences
-the <code>init</code> functions: it will not invoke the next one
-until the previous one has returned.
-</p>
-
-<p>
-To ensure reproducible initialization behavior, build systems are encouraged
-to present multiple files belonging to the same package in lexical file name
-order to a compiler.
-</p>
-
-
-<h3 id="Program_execution">Program execution</h3>
-<p>
-A complete program is created by linking a single, unimported package
-called the <i>main package</i> with all the packages it imports, transitively.
-The main package must
-have package name <code>main</code> and
-declare a function <code>main</code> that takes no
-arguments and returns no value.
-</p>
-
-<pre>
-func main() { … }
-</pre>
-
-<p>
-Program execution begins by initializing the main package and then
-invoking the function <code>main</code>.
-When that function invocation returns, the program exits.
-It does not wait for other (non-<code>main</code>) goroutines to complete.
-</p>
-
-<h2 id="Errors">Errors</h2>
-
-<p>
-The predeclared type <code>error</code> is defined as
-</p>
-
-<pre>
-type error interface {
- Error() string
-}
-</pre>
-
-<p>
-It is the conventional interface for representing an error condition,
-with the nil value representing no error.
-For instance, a function to read data from a file might be defined:
-</p>
-
-<pre>
-func Read(f *File, b []byte) (n int, err error)
-</pre>
-
-<h2 id="Run_time_panics">Run-time panics</h2>
-
-<p>
-Execution errors such as attempting to index an array out
-of bounds trigger a <i>run-time panic</i> equivalent to a call of
-the built-in function <a href="#Handling_panics"><code>panic</code></a>
-with a value of the implementation-defined interface type <code>runtime.Error</code>.
-That type satisfies the predeclared interface type
-<a href="#Errors"><code>error</code></a>.
-The exact error values that
-represent distinct run-time error conditions are unspecified.
-</p>
-
-<pre>
-package runtime
-
-type Error interface {
- error
- // and perhaps other methods
-}
-</pre>
-
-<h2 id="System_considerations">System considerations</h2>
-
-<h3 id="Package_unsafe">Package <code>unsafe</code></h3>
-
-<p>
-The built-in package <code>unsafe</code>, known to the compiler
-and accessible through the <a href="#Import_declarations">import path</a> <code>"unsafe"</code>,
-provides facilities for low-level programming including operations
-that violate the type system. A package using <code>unsafe</code>
-must be vetted manually for type safety and may not be portable.
-The package provides the following interface:
-</p>
-
-<pre class="grammar">
-package unsafe
-
-type ArbitraryType int // shorthand for an arbitrary Go type; it is not a real type
-type Pointer *ArbitraryType
-
-func Alignof(variable ArbitraryType) uintptr
-func Offsetof(selector ArbitraryType) uintptr
-func Sizeof(variable ArbitraryType) uintptr
-
-type IntegerType int // shorthand for an integer type; it is not a real type
-func Add(ptr Pointer, len IntegerType) Pointer
-func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType
-</pre>
-
-<!--
-These conversions also apply to type parameters with suitable core types.
-Determine if we can simply use core type insted of underlying type here,
-of if the general conversion rules take care of this.
--->
-
-<p>
-A <code>Pointer</code> is a <a href="#Pointer_types">pointer type</a> but a <code>Pointer</code>
-value may not be <a href="#Address_operators">dereferenced</a>.
-Any pointer or value of <a href="#Types">underlying type</a> <code>uintptr</code> can be
-<a href="#Conversions">converted</a> to a type of underlying type <code>Pointer</code> and vice versa.
-The effect of converting between <code>Pointer</code> and <code>uintptr</code> is implementation-defined.
-</p>
-
-<pre>
-var f float64
-bits = *(*uint64)(unsafe.Pointer(&f))
-
-type ptr unsafe.Pointer
-bits = *(*uint64)(ptr(&f))
-
-var p ptr = nil
-</pre>
-
-<p>
-The functions <code>Alignof</code> and <code>Sizeof</code> take an expression <code>x</code>
-of any type and return the alignment or size, respectively, of a hypothetical variable <code>v</code>
-as if <code>v</code> was declared via <code>var v = x</code>.
-</p>
-<p>
-The function <code>Offsetof</code> takes a (possibly parenthesized) <a href="#Selectors">selector</a>
-<code>s.f</code>, denoting a field <code>f</code> of the struct denoted by <code>s</code>
-or <code>*s</code>, and returns the field offset in bytes relative to the struct's address.
-If <code>f</code> is an <a href="#Struct_types">embedded field</a>, it must be reachable
-without pointer indirections through fields of the struct.
-For a struct <code>s</code> with field <code>f</code>:
-</p>
-
-<pre>
-uintptr(unsafe.Pointer(&s)) + unsafe.Offsetof(s.f) == uintptr(unsafe.Pointer(&s.f))
-</pre>
-
-<p>
-Computer architectures may require memory addresses to be <i>aligned</i>;
-that is, for addresses of a variable to be a multiple of a factor,
-the variable's type's <i>alignment</i>. The function <code>Alignof</code>
-takes an expression denoting a variable of any type and returns the
-alignment of the (type of the) variable in bytes. For a variable
-<code>x</code>:
-</p>
-
-<pre>
-uintptr(unsafe.Pointer(&x)) % unsafe.Alignof(x) == 0
-</pre>
-
-<p>
-A (variable of) type <code>T</code> has <i>variable size</i> if <code>T</code>
-is a <a href="#Type_parameter_declarations">type parameter</a>, or if it is an
-array or struct type containing elements
-or fields of variable size. Otherwise the size is <i>constant</i>.
-Calls to <code>Alignof</code>, <code>Offsetof</code>, and <code>Sizeof</code>
-are compile-time <a href="#Constant_expressions">constant expressions</a> of
-type <code>uintptr</code> if their arguments (or the struct <code>s</code> in
-the selector expression <code>s.f</code> for <code>Offsetof</code>) are types
-of constant size.
-</p>
-
-<p>
-The function <code>Add</code> adds <code>len</code> to <code>ptr</code>
-and returns the updated pointer <code>unsafe.Pointer(uintptr(ptr) + uintptr(len))</code>.
-The <code>len</code> argument must be of <a href="#Numeric_types">integer type</a> or an untyped <a href="#Constants">constant</a>.
-A constant <code>len</code> argument must be <a href="#Representability">representable</a> by a value of type <code>int</code>;
-if it is an untyped constant it is given type <code>int</code>.
-The rules for <a href="/pkg/unsafe#Pointer">valid uses</a> of <code>Pointer</code> still apply.
-</p>
-
-<p>
-The function <code>Slice</code> returns a slice whose underlying array starts at <code>ptr</code>
-and whose length and capacity are <code>len</code>.
-<code>Slice(ptr, len)</code> is equivalent to
-</p>
-
-<pre>
-(*[len]ArbitraryType)(unsafe.Pointer(ptr))[:]
-</pre>
-
-<p>
-except that, as a special case, if <code>ptr</code>
-is <code>nil</code> and <code>len</code> is zero,
-<code>Slice</code> returns <code>nil</code>.
-</p>
-
-<p>
-The <code>len</code> argument must be of <a href="#Numeric_types">integer type</a> or an untyped <a href="#Constants">constant</a>.
-A constant <code>len</code> argument must be non-negative and <a href="#Representability">representable</a> by a value of type <code>int</code>;
-if it is an untyped constant it is given type <code>int</code>.
-At run time, if <code>len</code> is negative,
-or if <code>ptr</code> is <code>nil</code> and <code>len</code> is not zero,
-a <a href="#Run_time_panics">run-time panic</a> occurs.
-</p>
-
-<h3 id="Size_and_alignment_guarantees">Size and alignment guarantees</h3>
-
-<p>
-For the <a href="#Numeric_types">numeric types</a>, the following sizes are guaranteed:
-</p>
-
-<pre class="grammar">
-type size in bytes
-
-byte, uint8, int8 1
-uint16, int16 2
-uint32, int32, float32 4
-uint64, int64, float64, complex64 8
-complex128 16
-</pre>
-
-<p>
-The following minimal alignment properties are guaranteed:
-</p>
-<ol>
-<li>For a variable <code>x</code> of any type: <code>unsafe.Alignof(x)</code> is at least 1.
-</li>
-
-<li>For a variable <code>x</code> of struct type: <code>unsafe.Alignof(x)</code> is the largest of
- all the values <code>unsafe.Alignof(x.f)</code> for each field <code>f</code> of <code>x</code>, but at least 1.
-</li>
-
-<li>For a variable <code>x</code> of array type: <code>unsafe.Alignof(x)</code> is the same as
- the alignment of a variable of the array's element type.
-</li>
-</ol>
-
-<p>
-A struct or array type has size zero if it contains no fields (or elements, respectively) that have a size greater than zero. Two distinct zero-size variables may have the same address in memory.
-</p>
diff --git a/cmd/golangorg/testdata/web.txt b/cmd/golangorg/testdata/web.txt
index cc78c63..4bd5cc9 100644
--- a/cmd/golangorg/testdata/web.txt
+++ b/cmd/golangorg/testdata/web.txt
@@ -342,14 +342,6 @@
GET https://go.dev/ref/spec
body contains <a id="assign_op">assign_op</a>
-# Issue 51686.
-GET https://go.dev/ref/spec
-body contains Version of March 10, 2022
-
-# Issue 51686.
-GET https://go.dev/doc/go1.17_spec
-body contains Version of Oct 15, 2021
-
GET https://golang.org/robots.txt
redirect == https://go.dev/robots.txt
