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Date: Wed, 20 Aug 2014 08:41:56 -0600
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To: Paul Dragoonis <dragoonis@gmail.com>
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: levim@php.net (Levi Morrison)

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 th=
e
>> 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 t=
ime
>> separating out the benefits of the AST (which I really like) and making
>> 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 for=
 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 w=
e
> can adapt the AST part or tweak another part to make this more consistent
> 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.

This really only affects strange situations, such as ones listed in the RFC=
.