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
diff --git a/doc/go_spec.html b/doc/go_spec.html
index 8cb257a..7819735 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -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 @@
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 = 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>
