Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:92050
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 74.125.82.51 as permitted sender)
MIME-Version: 1.0
Date: Fri, 1 Apr 2016 00:47:28 +0800
Message-ID: <CAGN=FiSPHpnBv2SHLWTQfrZUcOyqkDORn+rpuhDNSr+D+JGpCw@mail.gmail.com>
To: internals@lists.php.net
Content-Type: multipart/alternative; boundary=089e0122efbe878682052f5b0480
Subject: Copy On Write and Assign By Reference perform different on PHP5 and PHP7
From: liaohuqiu@gmail.com (Huqiu Liao)

--089e0122efbe878682052f5b0480
Content-Type: text/plain; charset=UTF-8

Hi, internals,

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.

---

We have a piece of simple code:

1    <?php
2    $i = 2;
3    $j = &$i;
4    echo (++$i) + (++$i);
On PHP5, it outputs 8, because:

$i is a reference, when we increase $i by ++i, it will change the zval
rather than make a copy, so line 4 will be 4 + 4 = 8. This is Assign By
Reference.

If we comment line 3, it will output 7, every time we change the value by
increasing it, PHP will make a copy, line 4 will be 3 + 4 = 7. This is Copy
On Write.

But in PHP7, it always outputs 7.

I've checked the changes in PHP7:
http://php.net/manual/en/migration70.incompatible.php, but I did not get
any clue.

Here is the result of the code on PHP5 / PHP7: https://3v4l.org/USTHR

And there is the link on Stackoverflow:
http://stackoverflow.com/questions/36338661/php-copy-on-write-and-assign-by-reference-perform-different-on-php5-and-php7

Thanks guys.


Best,


-- 

Huqiu Liao
http://www.liaohuqiu.net

--089e0122efbe878682052f5b0480--