spec: remove non-blocking channel operators
Add intended changes for close + closed, commented out.
R=golang-dev, niemeyer, r, gri1
CC=golang-dev
https://golang.org/cl/4013045
diff --git a/doc/go_spec.html b/doc/go_spec.html
index 51ece74..2d7f776 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1,5 +1,5 @@
<!-- title The Go Programming Language Specification -->
-<!-- subtitle Version of January 26, 2011 -->
+<!-- subtitle Version of January 27, 2011 -->
<!--
TODO
@@ -3027,28 +3027,7 @@
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.
</p>
-<p>
-If the send operation appears in an expression context, the value
-of the expression is a boolean and the operation is non-blocking.
-The value of the boolean reports true if the communication succeeded,
-false if it did not. (The channel and
-the expression to be sent are evaluated regardless.)
-These two examples are equivalent:
-</p>
-<pre>
-ok := ch <- 3
-if ok { print("sent") } else { print("not sent") }
-
-if ch <- 3 { print("sent") } else { print("not sent") }
-</pre>
-
-<p>
-In other words, if the program tests the value of a send operation,
-the send is non-blocking and the value of the expression is the
-success of the operation. If the program does not test the value,
-the operation blocks until it succeeds.
-</p>
<p>
The receive operation uses the prefix unary operator "<-".
The value of the expression is the value received, whose type
@@ -3073,8 +3052,11 @@
<-strobe // wait until clock pulse
</pre>
+<!--
+ TODO(rsc): Add after a release or two without any x,ok := <-c.
+
<p>
-If a receive expression is used in an assignment or initialization of the form
+A receive expression used in an assignment or initialization of the form
</p>
<pre>
@@ -3084,14 +3066,13 @@
</pre>
<p>
-the receive operation becomes non-blocking.
-If the operation can proceed, the boolean variable
-<code>ok</code> will be set to <code>true</code>
-and the value stored in <code>x</code>; otherwise
-<code>ok</code> is set
-to <code>false</code> and <code>x</code> is set to the
-zero value for its type (§<a href="#The_zero_value">The zero value</a>).
+yields an additional result.
+The boolean variable <code>ok</code> indicates whether
+the received value was sent on the channel (<code>true</code>)
+or is a <a href="#The_zero_value">zero value</a> returned
+because the channel is closed and empty (<code>false</code>).
</p>
+-->
<p>
Except in a communications clause of a <a href="#Select_statements">select statement</a>,
@@ -4097,6 +4078,9 @@
CommClause = CommCase ":" { Statement ";" } .
CommCase = "case" ( SendExpr | RecvExpr) | "default" .
SendExpr = Expression "<-" Expression .
+<!-- TODO(rsc):
+RecvExpr = [ Expression [ "," Expression ] ( "=" | ":=" ) ] "<-" Expression .
+-->
RecvExpr = [ Expression ( "=" | ":=" ) ] "<-" Expression .
</pre>
@@ -4128,6 +4112,7 @@
If multiple cases can proceed, a pseudo-random fair choice is made to decide
which single communication will execute.
<p>
+<!-- TODO(rsc): s/variable/& or &s/ -->
The receive case may declare a new variable using a
<a href="#Short_variable_declarations">short variable declaration</a>.
</p>
@@ -4140,6 +4125,14 @@
print("received ", i1, " from c1\n")
case c2 <- i2:
print("sent ", i2, " to c2\n")
+<!-- TODO(rsc): add , c3 to channel list above too
+case i3, ok := <-c3:
+ if ok {
+ print("received ", i3, " from c3\n")
+ } else {
+ print("c3 is closed\n")
+ }
+-->
default:
print("no communication\n")
}
@@ -4393,6 +4386,7 @@
BuiltinArgs = Type [ "," ExpressionList ] | ExpressionList .
</pre>
+<!-- TODO(rsc): s/.and.closed//g -->
<h3 id="Close_and_closed">Close and closed</h3>
<p>
@@ -4402,6 +4396,11 @@
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.
+
+<!-- TODO(rsc): delete next sentence, replace with
+ The multi-valued <a href="#Communication_operators">receive operation</a>
+ returns a received value along with an indication of whether the channel is closed.
+-->
After at least one such zero value has been
received, <code>closed(c)</code> returns true.
</p>
