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spec: clarify when range x does not evaluate x

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Fixes #4644.

R=r, adonovan
CC=golang-dev
https://golang.org/cl/7307083
This commit is contained in:
Russ Cox 2013-02-15 14:39:28 -05:00
parent 318309a51f
commit 61e02ee901
1 changed files with 11 additions and 5 deletions
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16
doc/go_spec.html
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@ -4377,9 +4377,15 @@ the range clause is equivalent to the same clause with only the first variable p
</p>
<p>
The range expression is evaluated once before beginning the loop
except if the expression is an array, in which case, depending on
the expression, it might not be evaluated (see below).
The range expression is evaluated once before beginning the loop,
with one exception. If the range expression is an array or a pointer to an array
and only the first iteration value is present, only the range expression's
length is evaluated; if that length is constant by definition
(see §<a href="#Length_and_capacity">Length and capacity</a>),
the range expression itself will not be evaluated.
</p>
<p>
Function calls on the left are evaluated once per iteration.
For each iteration, iteration values are produced as follows:
</p>
@ -4396,8 +4402,8 @@ channel c chan E, &lt;-chan E element e E
<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. As a special
case, if only the first iteration variable is present, the range loop produces
values are produced in increasing order, starting at element index 0.
If only the first iteration variable is present, the range loop produces
iteration values from 0 up to <code>len(a)</code> and does not index into the array
or slice itself. For a <code>nil</code> slice, the number of iterations is 0.
</li>