code review 6246045: spec: clarify evaluation order of "i, x[i] = range ..."

spec: clarify evaluation order of "i, x[i] = range ..."

Part of fix for issue 3464.

[gri, 2012-05-24 00:46:14]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go

[rsc, 2012-05-24 00:47:26]

I think you mean "or a for statement's range clause".  More than the
range expression appears on the rhs.

[gri, 2012-05-24 00:52:42]

On Wed, May 23, 2012 at 5:47 PM, Russ Cox <rsc@golang.org> wrote:
> I think you mean "or a for statement's range clause".  More than the
> range expression appears on the rhs.

"of a for statement's range clause" I buy. that's the rhs I care about

[gri, 2012-05-24 00:55:14]

Hello golang-dev@googlegroups.com, rsc@golang.org (cc:
golang-dev@googlegroups.com),

Please take another look.

[rsc, 2012-05-24 00:55:31]

the "or" is just part of the sentence, because it's the last of a long list.
but yes, i think we agree.

[rsc, 2012-05-24 00:59:28]

I stll disagree that the range expression of a for clause is a 'single
multi-valued expression'.  Quoting elsewhere in the spec, 'The range
expression is evaluated once before beginning the loop'.  The new text
overloads that phrase.

Maybe instead of trying to write text we should just leave it at the example?

Russ

[gri, 2012-05-24 01:05:33]

Hello golang-dev@googlegroups.com, rsc@golang.org (cc:
golang-dev@googlegroups.com),

Please take another look.

[rsc, 2012-05-24 01:07:06]

LGTM

Sorry for being pedantic.

[aam, 2012-05-24 01:07:15]

Sorry this is off-topic, but don't you mean "Version of May 24, 2012"?

[iant, 2012-05-24 03:37:20]

LGTM

http://codereview.appspot.com/6246045/diff/15001/doc/go_spec.html
File doc/go_spec.html (right):

http://codereview.appspot.com/6246045/diff/15001/doc/go_spec.html#newcode3
doc/go_spec.html:3: "Subtitle": "Version of March 24, 2012",
s/March/May/

[r, 2012-05-24 03:43:03]

LGTM

http://codereview.appspot.com/6246045/diff/15001/doc/go_spec.html
File doc/go_spec.html (right):

http://codereview.appspot.com/6246045/diff/15001/doc/go_spec.html#newcode3905
doc/go_spec.html:3905: // so i == 0, x == []int{3, 5, 3} at end
// After this loop, i ==0 and x == []int{3, 5, 3}

[r, 2012-05-24 03:43:38]

s/==0/== 0/ of course

[gri, 2012-05-24 17:59:52]

*** Submitted as http://code.google.com/p/go/source/detail?r=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
http://codereview.appspot.com/6246045

[cw, 2012-05-24 22:32:49]

Does that also clarify:

        x := []int{1, 0}

        x[x[0]], x[x[1]] = 5, 6

[gri, 2012-05-24 23:01:05]

On Thu, May 24, 2012 at 3:32 PM, Chris Wedgwood <cw@f00f.org> wrote:
> Does that also clarify:
>
>        x := []int{1, 0}
>
>        x[x[0]], x[x[1]] = 5, 6

This case was not disputed here. All indices are evaluated before any
assignments are happening. The result is well-defined (x == []int{6,
5} afterwards).
- gri