Edit report at https://bugs.php.net/bug.php?id=71217&edit=1
ID: 71217
Updated by: [email protected]
Reported by: bugs dot php dot net at ss dot st dot tc
Summary: foreach() with inline assignment doesn't keep
references
-Status: Open
+Status: Not a bug
Type: Bug
Package: Scripting Engine problem
Operating System: Linux, OSX
PHP Version: 7.0.1
Block user comment: N
Private report: N
New Comment:
As pointed out by inefedor, the previous behavior was a bug and the new behavior is correct. Simple assignment expressions return *values*, not references, so you'll be operating on a copy.
The only type of assignment expression that returns a reference is a by-reference assignment. If you iterate other something like $ref =& $source, you will iterate over a reference to $ref and $source.
As to the suggestion that an error shall be thrown: This is not done for the same reason why temporary expressions were allowed as arguments for by-ref foreach in the first place in PHP 5.5: By-reference iteration can be meaningful for non-reference expressions if a) the expression is an Iterator supporting by-reference iteration, b) the expression is a simple object or c) the expression is an array containing reference elements. In all of these cases modifications performed in a by-ref foreach loop can be observable.
Previous Comments:
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[2015-12-24 21:55:25] bugs dot php dot net at ss dot st dot tc
I see @inefedor's point. Turns out we've been using this bug for ages (as a nice "feature"). The worst thing here is that such constructions are spread all over our codebase, especially case #3.
But I strongly agree with another expressed opinion here: I'd also expect leftmost part of an assignment to act as a result of an assignment operation (and therefore to be iterated, instead of its copy (or whatever is a result of assignment operation)).
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[2015-12-24 21:21:31] php at etc dot chkgo dot com
@inefedor Well, buildding such a constriction, I expect that assignment would be made before the loop starts. As for the reference, I expect it to be made to the items I iterate, not the assignment. Assignment itself can't be iterated. So if foreach is provided with unacceptable argument, why not throw an error then?
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[2015-12-24 20:53:44] inefedor at gmail dot com
There's a few kinds of expressions from which you can meaningfully take a reference: it's `$var` (just calling a variable by name), `$var->prop`, `$var["key"]` and probably some flavors of variable variables (e.g. `$$var`).
But assignment is not an expression that could be used as a reference. Now in 5.x it worked, probably by mistake and it would be a BC break to remove it from 5.x. But it was fixed in PHP 7.
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[2015-12-24 20:26:10] php at etc dot chkgo dot com
Faced the same problem in a part of function results assignment right in foreach and changing iterated items by reference. Got unexpected behavior on PHP 7.0.0 and 7.0.1 but seemed working fine on 5.6. /Gentoo
So it was pretty much as described in the ticket. My vote.
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[2015-12-24 20:07:43] bugs dot php dot net at ss dot st dot tc
Description:
------------
When an inline assignment of array_expression is done right in foreach() statement, all further references to iterated array items seem to become their copies.
I believe both PHP 5.6 and 7 are affected, yet still they behave differently.
Tested on PHP 5.6.12, 5.6.16, 7.0.0, 7.0.1.
Test script:
---------------
<?php
# source array
$source = [ 'subarray' => ['item' => 'old value ---'] ];
# $ref1 is assigned to $source right in the foreach()
foreach ( $ref1 = $source as &$subarray ) {
$subarray['item'] = 'NEW value';
echo $subarray['item'], PHP_EOL;
echo $ref1['subarray']['item'], PHP_EOL;
}
echo PHP_EOL;
# $ref2 is assigned to $source normally, as a separate operation
$ref2 = $source;
foreach ( $ref2 as &$subarray ) {
$subarray['item'] = 'NEW value';
echo $subarray['item'], PHP_EOL;
echo $ref2['subarray']['item'], PHP_EOL;
}
echo PHP_EOL;
########################################
# similar to $source array, but implemented using a function
function getSource() {
return [ 'subarray' => ['item' => 'old value ---'] ];
}
# $ref3 is assigned to result of getSource() right in the foreach()
foreach ( $ref3 = getSource() as &$subarray ) {
$subarray['item'] = 'NEW value';
echo $subarray['item'], PHP_EOL;
echo $ref3['subarray']['item'], PHP_EOL;
}
echo PHP_EOL;
# $ref4 is a "normal" reference to a result of getSource()
$ref4 = getSource();
foreach ( $ref4 as &$subarray ) {
$subarray['item'] = 'NEW value';
echo $subarray['item'], PHP_EOL;
echo $ref4['subarray']['item'], PHP_EOL;
}
Expected result:
----------------
both PHP 5 and 7:
NEW value
NEW value
NEW value
NEW value
NEW value
NEW value
NEW value
NEW value
Actual result:
--------------
PHP 7:
NEW value
old value ---
NEW value
NEW value
NEW value
old value ---
NEW value
NEW value
PHP 5:
NEW value
old value ---
NEW value
NEW value
NEW value
NEW value
NEW value
NEW value
------------------------------------------------------------------------
--
Edit this bug report at https://bugs.php.net/bug.php?id=71217&edit=1
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