Bug #71217 [Opn->Nab]: foreach() with inline assignment doesn't keep references

Edit report at https://bugs.php.net/bug.php?id=71217&edit=1 ID: 71217 Updated by: nikic@php.net 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: ------------------------------------------------------------------------ [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)). ------------------------------------------------------------------------ [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? ------------------------------------------------------------------------ [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. ------------------------------------------------------------------------ [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. ------------------------------------------------------------------------ [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