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go spec: simplify section on channel types

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R=rsc, iant, r
CC=golang-dev
https://golang.org/cl/1171041
This commit is contained in:
Robert Griesemer 2010-05-07 18:22:40 -07:00
parent f023e859cf
commit 56ca697269
1 changed files with 20 additions and 22 deletions
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42
doc/go_spec.html
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@ -1,5 +1,5 @@
<!-- title The Go Programming Language Specification -->
<!-- subtitle Version of May 4, 2010 -->
<!-- subtitle Version of May 7, 2010 -->
<!--
Todo
@ -1154,16 +1154,26 @@ A value of channel type may be <code>nil</code>.
</p>
<pre class="ebnf">
ChannelType = Channel | SendChannel | RecvChannel .
Channel = "chan" ElementType .
SendChannel = "chan" "&lt;-" ElementType .
RecvChannel = "&lt;-" "chan" ElementType .
ChannelType = ( "chan" [ "&lt;-" ] | "&lt;-" "chan" ) ElementType .
</pre>
<p>
To avoid a parsing ambiguity in cases such as <code>chan&lt;- chan int</code>,
the Channel production's ElementType cannot be a RecvChannel.
To construct such a type, parenthesize the RecvChannel first.
The <code>&lt;-</code> operator specifies the channel <i>direction</i>,
<i>send</i> or <i>receive</i>. If no direction is given, the channel is
<i>bi-directional</i>.
A channel may be constrained only to send or only to receive by
<a href="#Conversions">conversion</a> or <a href="#Assignments">assignment</a>.
</p>
<pre>
chan T // can be used to send and receive values of type T
chan&lt;- float // can only be used to send floats
&lt;-chan int // can only be used to receive ints
</pre>
<p>
The <code>&lt;-</code> operator associates with the leftmost <code>chan</code>
possible:
</p>
<pre>
@ -1173,22 +1183,10 @@ chan&lt;- &lt;-chan int // same as chan&lt;- (&lt;-chan int)
chan (&lt;-chan int)
</pre>
<p>
Upon creation, a channel can be used both to send and to receive values.
By conversion or assignment, a channel may be constrained only to send or
to receive. This constraint is called a channel's <i>direction</i>; either
<i>send</i>, <i>receive</i>, or <i>bi-directional</i> (unconstrained).
</p>
<pre>
chan T // can be used to send and receive values of type T
chan&lt;- float // can only be used to send floats
&lt;-chan int // can only be used to receive ints
</pre>
<p>
The value of an uninitialized channel is <code>nil</code>. A new, initialized channel
value can be made using the built-in function <code>make</code>,
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 capacity as arguments:
</p>