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Date: Thu, 31 Mar 2016 18:52:24 -0700
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To: Huqiu Liao <liaohuqiu@gmail.com>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Copy On Write and Assign By Reference perform different
 on PHP5 and PHP7
From: pollita@php.net (Sara Golemon)

On Thu, Mar 31, 2016 at 9:47 AM, Huqiu Liao <liaohuqiu@gmail.com> wrote:
> I have a question about Assign By Reference and I posted on StackOverflow,
> I'd like to know the reason behind it, and I did not get any this kind of
> answer, can anyone give me some clues.
>
Are you asking out of curiosity? Or because you think a new bug has
been introduced in PHP7?

If the latter, I'd respond by pointing out that the behavior of using
multiple operations with side-effects (like pre/post inc/dec) is
defined as undefined.  That is, while the PHP reference implementation
may give you a particular result, you should not rely on that result.

If the former, and you're just curious why, it comes down to a very
fundamental change in the way PHP7 deals with references.  I'd
recommend reading Nikita's writeup of the differences between PHP 5
and PHP 7 variables at:
https://nikic.github.io/2015/05/05/Internal-value-representation-in-PHP-7-part-1.html

-Sara