spec: comma-ok expressions return untyped boolean 2nd result
Technically a language change, this cleanup is a completely
backward compatible change that brings the boolean results
of comma-ok expressions in line with the boolean results of
comparisons: they are now all untyped booleans.
The implementation effort should be minimal (less than a
handfull lines of code, depending how well factored the
implementation of comma-ok expressions is).
Fixes #8189.
LGTM=iant, r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/112320045
diff --git a/doc/go_spec.html b/doc/go_spec.html
index 0200762..a32fa45 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
- "Subtitle": "Version of July 14, 2014",
+ "Subtitle": "Version of August 5, 2014",
"Path": "/ref/spec"
}-->
@@ -2626,7 +2626,7 @@
<p>
An index expression on a map <code>a</code> of type <code>map[K]V</code>
-may be used in an assignment or initialization of the special form
+used in an <a href="#Assignments">assignment</a> or initialization of the special form
</p>
<pre>
@@ -2636,11 +2636,9 @@
</pre>
<p>
-where the result of the index expression is a pair of values with types
-<code>(V, bool)</code>. In this form, the value of <code>ok</code> is
+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. The value of <code>v</code> is the value
-<code>a[x]</code> as in the single-result form.
+<code>false</code> otherwise.
</p>
<p>
@@ -2825,7 +2823,7 @@
</pre>
<p>
-If a type assertion is used in an <a href="#Assignments">assignment</a> or initialization of the form
+A type assertion used in an <a href="#Assignments">assignment</a> or initialization of the special form
</p>
<pre>
@@ -2835,13 +2833,10 @@
</pre>
<p>
-the result of the assertion is a pair of values with types <code>(T, bool)</code>.
-If the assertion holds, the expression returns the pair <code>(x.(T), true)</code>;
-otherwise, the expression returns <code>(Z, false)</code> where <code>Z</code>
-is the <a href="#The_zero_value">zero value</a> for type <code>T</code>.
+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 run-time panic occurs in this case.
-The type assertion in this construct thus acts like a function call
-returning a value and a boolean indicating success.
</p>
@@ -3423,7 +3418,7 @@
</pre>
<p>
-A receive expression used in an assignment or initialization of the form
+A receive expression used in an <a href="#Assignments">assignment</a> or initialization of the special form
</p>
<pre>
@@ -3433,7 +3428,7 @@
</pre>
<p>
-yields an additional result of type <code>bool</code> reporting whether the
+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
