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[release-branch.go1] spec: clarify evaluation order of "i, x[i] = range ..."

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««« backport 1c4d1ba268ca
spec: clarify evaluation order of "i, x[i] = range ..."

Part of fix for issue 3464.

R=golang-dev, rsc, mirtchovski, iant, r
CC=golang-dev
https://golang.org/cl/6246045

»»»
This commit is contained in:
Robert Griesemer 2012-06-13 16:24:16 -04:00
parent b260999d4c
commit ea2a0ad508
1 changed files with 14 additions and 3 deletions
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17
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
"Subtitle": "Version of March 17, 2012",
"Subtitle": "Version of May 24, 2012",
"Path": "/ref/spec"
}-->
@ -3866,7 +3866,11 @@ x, _ = f() // ignore second value returned by f()
In the second form, the number of operands on the left must equal the number
of expressions on the right, each of which must be single-valued, and the
<i>n</i>th expression on the right is assigned to the <i>n</i>th
operand on the left. The assignment proceeds in two phases.
operand on the left.
</p>
<p>
The assignment proceeds in two phases.
First, the operands of <a href="#Indexes">index expressions</a>
and <a href="#Address_operators">pointer indirections</a>
(including implicit pointer indirections in <a href="#Selectors">selectors</a>)
@ -3885,13 +3889,20 @@ i, x[i] = 1, 2 // set i = 1, x[0] = 2
i = 0
x[i], i = 2, 1 // set x[0] = 2, i = 1
x[0], x[0] = 1, 2 // set x[0] = 1, then x[0] = 2 (so x[0] = 2 at end)
x[0], x[0] = 1, 2 // set x[0] = 1, then x[0] = 2 (so x[0] == 2 at end)
x[1], x[3] = 4, 5 // set x[1] = 4, then panic setting x[3] = 5.
type Point struct { x, y int }
var p *Point
x[2], p.x = 6, 7 // set x[2] = 6, then panic setting p.x = 7
i = 2
x = []int{3, 5, 7}
for i, x[i] = range x { // set i, x[2] = 0, x[0]
break
}
// after this loop, i == 0 and x == []int{3, 5, 3}
</pre>
<p>