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spec: disallow goto into blocks

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R=gri, r, r
CC=golang-dev
https://golang.org/cl/4631045
This commit is contained in:
Russ Cox 2011-06-17 12:49:04 -04:00
parent 21e75da486
commit f4c7db0ed9
1 changed files with 26 additions and 7 deletions
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33
doc/go_spec.html
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@ -1,5 +1,5 @@
<!-- title The Go Programming Language Specification -->
<!-- subtitle Version of June 13, 2011 -->
<!-- subtitle Version of June 17, 2011 -->
<!--
TODO
@ -4393,8 +4393,8 @@ goto Error
<p>
Executing the "goto" statement must not cause any variables to come into
scope that were not already in scope at the point of the goto. For
instance, this example:
<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>
@ -4406,9 +4406,29 @@ L:
<p>
is erroneous because the jump to label <code>L</code> skips
the creation of <code>v</code>.
<!--
(<span class="alert">TODO: Eliminate in favor of used and not set errors?</span>)
-->
</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 &gt; 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>
@ -5244,7 +5264,6 @@ The following minimal alignment properties are guaranteed:
<span class="alert">
<h2 id="Implementation_differences">Implementation differences - TODO</h2>
<ul>
<li>The restriction on <code>goto</code> statements and targets (no intervening declarations) is not honored.</li>
<li><code>len(a)</code> is only a constant if <code>a</code> is a (qualified) identifier denoting an array or pointer to an array.</li>
<li><code>nil</code> maps are not treated like empty maps.</li>
<li>Trying to send/receive from a <code>nil</code> channel causes a run-time panic.</li>