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Date: Thu, 21 Aug 2014 08:16:55 +0100
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To: Levi Morrison <levim@php.net>
Cc: Andi Gutmans <andi@zend.com>, Nikita Popov <nikita.ppv@gmail.com>, 
	PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [VOTE] Abstract Syntax Tree
From: dragoonis@gmail.com (Paul Dragoonis)

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On Wed, Aug 20, 2014 at 3:41 PM, Levi Morrison <levim@php.net> wrote:

> On Wed, Aug 20, 2014 at 7:30 AM, Paul Dragoonis <dragoonis@gmail.com>
> wrote:
> > On Tue, Aug 19, 2014 at 3:32 AM, Andi Gutmans <andi@zend.com> wrote:
> >
> >> Hi Nikita,
> >>
> >> I reviewed the AST RFC on my way to vote but there was something that
> >> wasn=E2=80=99t clear to me.
> >> This patch introduces some semantic/behavioral changes in addition to
> the
> >> AST.
> >> Are these as a side-effect of how AST was implemented? Or are they
> >> unrelated to the AST patch?
> >> I think some of them make sense but I=E2=80=99m having a bit of a hard=
 time
> >> separating out the benefits of the AST (which I really like) and makin=
g
> >> other changes to semantics w/o really understanding if they are
> >> side-effects and we have no choice vs. we=E2=80=99re trying to solve f=
or two
> >> separate items in one RFC.
> >> Any BC breaks here we think could bite us?
> >>
> >
> > Hi Nikita,
> >
> > I second some of Andi's concerns about behavioural changes, some things
> > working from right-to-left and not left-to-right. Are these things that
> we
> > can adapt the AST part or tweak another part to make this more consiste=
nt
> > with previous versions of PHP.
>
> I just had a chat with Paul about this, and there was a
> misunderstanding about what this RFC actually does regarding
> left-to-right evaluation on list() constructs. I also saw this
> misunderstanding in a few other places, so it seems to be a common
> misunderstanding.
>
> Under the proposed changes as well as in PHP 5.x, the end result of
> the following is the same:
>
>     list($a, $b) =3D array(1, 2);
>
> $a will be 1 and $b will be 2. Again, this hasn't changed. The
> difference is that in PHP 5.x the variable $b will be assigned 2
> before $a is assigned 1; under these changes $a will be assigned 1
> first and then $b will be assigned 2.
>

I'm happy with this behaviour and agree that the AST version is what I
would expect, my confusion was that I thought PHP 5.x was 1,2 and the AST
was 2,1 which it of course is not the case. Now you could see why I raised
concerns about this in the first place.


>
> This really only affects strange situations, such as ones listed in the
> RFC.
>

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