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add a section about order of evaluation

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DELTA=32  (29 added, 2 deleted, 1 changed)
OCL=27197
CL=27469
This commit is contained in:
Rob Pike 2009-04-14 20:10:49 -07:00
parent 935953a9f8
commit c956e90913
1 changed files with 30 additions and 3 deletions
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33
doc/go_spec.html
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@ -26,8 +26,6 @@ Todo's:
[ ] cleanup: 6g allows: interface { f F } where F is a function type.
fine, but then we should also allow: func f F {}, where F is a function type.
[ ] decide if and what to write about evaluation order of tuple assignments
[ ] decide if and what to write about evaluation order of composite literal
elements (single expressions, (key:value) pairs)
Wish list:
[ ] enum facility (enum symbols that are not mixable with ints) or some other
@ -126,6 +124,8 @@ Closed:
a for loop that is following, and can break L be used inside it?
[x] there is some funniness regarding ';' and empty statements and label decls
[x] cleanup convert() vs T() vs x.(T) - convert() should go away?
[x] decide if and what to write about evaluation order of composite literal
elements (single expressions, (key:value) pairs)
-->
@ -162,7 +162,7 @@ Expression = Alternative { "|" Alternative } .
Alternative = Term { Term } .
Term = production_name | token [ "..." token ] | Group | Option | Repetition .
Group = "(" Expression ")" .
Option = "[" Expression ")" .
Option = "[" Expression "]" .
Repetition = "{" Expression "}" .
</pre>
@ -2983,6 +2983,33 @@ Also it may be possible to make typed constants more like variables, at the cost
overflow etc. errors being caught.
</p>
<h3>Order of evaluation</h3>
<p>
When evaluating the elements of an assignment or expression,
all function calls, method calls and
communication operations are evaluated in lexical left-to-right
order. Otherwise, the order of evaluation is unspecified.
</p>
<p>
For example, while evaluating the arguments for this call
to function <code>f</code>,
</p>
<pre>
f(g(), h() + x[i()], <-c)
</pre>
<p>
the call to <code>g()</code> happens before the call to <code>h()</code>,
which happens before the call to <code>i()</code>, all of
of which happen before receiving the value from the channel
<code>c</code>.
However, the order of those events compared to the evaluation of
<code>f</code>, the evaluation of <code>x</code>, and the indexing
of <code>x</code> by the return value of
<code>i()</code> is not specified.
</p>
<hr/>
<h2>Statements</h2>