Bug #75629 [Com]: Object property references are replaced by references created in functions

Edit report at https://bugs.php.net/bug.php?id=75629&edit=1 ID: 75629 Comment by: ocramius@php.net Reported by: ocramius@php.net Summary: Object property references are replaced by references created in functions Status: Feedback Type: Bug Package: Scripting Engine problem Operating System: Linux x64 PHP Version: Irrelevant Block user comment: N Private report: N New Comment: As discussed with Nikic, this issue is likely a misunderstanding in how references work. References are bi-directional, and have to be maintained until necessary. In the test case above, the reference becomes unnecessary as soon as the closure execution ends, but it is to be kept when pushing it to an array. This specific line is actually acting on a reference, and writing a clone to a reference, therefore overwriting both objects: $this->referencedProperty = clone $this->referencedProperty A solution here is to de-reference the value by moving the reference: ``` $ref = & $this->referencedProperty; unset($this->referencedProperty); $this->referencedProperty = clone $ref; ``` I'm still not convinced that this is right, as it basically makes references a complete nightmare to work it (not that it was a pleasure before this). Previous Comments: ------------------------------------------------------------------------ [2017-12-05 12:00:55] ocramius@php.net @nikic two incorrect things are going on here: 1. the referencedProperty is cloned too here (via __clone), so it should be a new instance anyway 2. the Container#$referencedProperty is never a reference itself, but it is passed by reference to the $loadFieldByReference() closure and stored in $references ------------------------------------------------------------------------ [2017-12-05 11:04:34] nikic@php.net Try clarify, is the behavior you object to the fact that PHP preserves references while cloning? https://3v4l.org/c4iov ------------------------------------------------------------------------ [2017-12-05 09:24:11] ocramius@php.net Causes https://github.com/Ocramius/ProxyManager/pull/396 (original source of the bug) ------------------------------------------------------------------------ [2017-12-05 09:21:00] ocramius@php.net Description: ------------ See https://3v4l.org/BNDsu The PHP engine seems to globally replace references of object properties when new object property references are created in a by-ref function call. The problem occurs when defining a by-ref parameter in a function and then calling it with an object property: function foo(& $param) { // keep a non-gc reference to $param here and things will break } The attached test case demonstrates the issue by using clone and an array of references. The same example works when the references are kept in another object. Possible causes here are: * clone is misbehaving * references are misbehaving overall (YIKES!) * references created in functions are cached somewhere Test script: --------------- --TEST-- Keeping a reference to an object property in an array should not override existing references ?> --FILE-- <?php class Container { /** @var \stdClass|null */ public $referencedProperty; public function __clone() { $this->referencedProperty = clone $this->referencedProperty; } } $references = []; $container = new Container(); $loadFieldByReference = function (& $referencedProperty) use (& $references) { $referencedProperty = new \stdClass(); $references[] = & $referencedProperty; }; $loadFieldByReference($container->referencedProperty); $container->referencedProperty->publicProperty = 123; $clone = clone $container; $clone->referencedProperty->publicProperty = 234; echo $container->referencedProperty->publicProperty, "\n"; echo $clone->referencedProperty->publicProperty, "\n"; echo $container->referencedProperty === $clone->referencedProperty ? "same\n" : "not same\n"; ?> --EXPECT-- 123 234 not same ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=75629&edit=1