PHP7 / foreach / references / ugly code / discrepancy to PHP 5.6 View as Markdown

Here’s a 3v4l demonstrating this too:

https://3v4l.org/OXAd3 https://3v4l.org/OXAd3

Hi,

I'm having a cause of slightly ugly code that runs differently from PHP 5.6
to PHP 7 and I don't think this difference is documented, nor expected. As
I'm not sure whether this is an intended change or not, I'm asking here
firstr before making a bug report.

The code in question is

---

$b = [1, 2, 3];

foreach($b ?: [] as &$v){
$v = $v*2;
unset($v);
}

var_dump($b);

in PHP7, this produces

array(3) {
[0] =>
int(1)
[1] =>
int(2)
[2] =>
int(3)
}

whereas in PHP 5.6 and earlier, this produces

array(3) {
[0] =>
int(2)
[1] =>
int(4)
[2] =>
int(6)
}

what scares me about this is that in order to get the old behaviour in PHP7
back, you just have to get rid of the ?: operator:

foreach($b as &$v){

is fine

foreach($b ?: [] as &$v){

is not.

I guess this is related to
http://php.net/manual/en/migration70.incompatible.php#migration70.incompatible.foreach.by-value
or
http://php.net/manual/en/migration70.incompatible.php#migration70.incompatible.foreach.by-ref,
but I'm not entirely sure whether this is actually intended behaviour -
it's certainly unexpected to me that applying ?: now always makes a copy
whereas before it didn't.

Philip

--
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Giesshübelstrasse 62c, Postfach 1966, 8021 Zürich
Tel. +41 43 544 09 60, Mobile +41 79 341 01 99
info@sensational.ch, http://www.sensational.ch

On Tue, Nov 10, 2015 at 11:48 AM, Philip Hofstetter <
phofstetter@sensational.ch> wrote:

Hi,
...snip...
I guess this is related to

http://php.net/manual/en/migration70.incompatible.php#migration70.incompatible.foreach.by-value
or

http://php.net/manual/en/migration70.incompatible.php#migration70.incompatible.foreach.by-ref
,
but I'm not entirely sure whether this is actually intended behaviour -
it's certainly unexpected to me that applying ?: now always makes a copy
whereas before it didn't.

The issue may not be with foreach, but instead with the ?: ternary or the
optimizer. Maybe either:

1. It's a side-effect of merging the ZEND_QM_ASSIGN and ZEND_QM_ASSIGN_VAR
   op codes. (See PHP 5.6 ?: op code definitions
   https://github.com/php/php-src/blob/PHP-5.6/Zend/zend_vm_def.h#L4977-L5021
   and Same for PHP 7.0
   https://github.com/php/php-src/blob/master/Zend/zend_vm_def.h#L6945-L6977
   .)

2. The optimizer isn't handling the foreach scenario. (See Block pass
   optimizer code
   https://github.com/php/php-src/blob/master/ext/opcache/Optimizer/block_pass.c#L574-L593
   .)

I don't see any change notes for either, so I'm guessing this is a bug.

bishop

On Tue, Nov 10, 2015 at 5:48 PM, Philip Hofstetter <
phofstetter@sensational.ch> wrote:

Hi,

I'm having a cause of slightly ugly code that runs differently from PHP 5.6
to PHP 7 and I don't think this difference is documented, nor expected. As
I'm not sure whether this is an intended change or not, I'm asking here
firstr before making a bug report.

The code in question is

---

$b = [1, 2, 3];

foreach($b ?: [] as &$v){
$v = $v*2;
unset($v);
}

var_dump($b);

in PHP7, this produces

array(3) {
[0] =>
int(1)
[1] =>
int(2)
[2] =>
int(3)
}

whereas in PHP 5.6 and earlier, this produces

array(3) {
[0] =>
int(2)
[1] =>
int(4)
[2] =>
int(6)
}

what scares me about this is that in order to get the old behaviour in PHP7
back, you just have to get rid of the ?: operator:

foreach($b as &$v){

is fine

foreach($b ?: [] as &$v){

is not.

I guess this is related to

http://php.net/manual/en/migration70.incompatible.php#migration70.incompatible.foreach.by-value
or

http://php.net/manual/en/migration70.incompatible.php#migration70.incompatible.foreach.by-ref
,
but I'm not entirely sure whether this is actually intended behaviour -
it's certainly unexpected to me that applying ?: now always makes a copy
whereas before it didn't.

This is a bug in PHP 5, which has been fixed in PHP 7 as a side-effect of
other changes. The new behavior is correct. This issue is tracked at
https://bugs.php.net/bug.php?id=70857.

Nikita