Bug #79377 [Nab]: Property is not cloned with clone

Edit report at https://bugs.php.net/bug.php?id=79377&edit=1 ID: 79377 Updated by: requinix@php.net Reported by: mvorisek at mvorisek dot cz Summary: Property is not cloned with clone Status: Not a bug Type: Bug Package: Scripting Engine problem Operating System: Any PHP Version: 7.4.3 Block user comment: N Private report: N New Comment: Here's a more in-depth explanation of references and PHP's variable/memory management: http://www.phpinternalsbook.com/php5/zvals/memory_management.html > Outside cloning this approach makes sense and can not be even noticed, but shouln't clone > create a (lazy - > standard copy-on-write) copy of each scalar/array property no matter if this property was > referenced or not? That's debatable. Copying the reference makes sense because the property itself is a reference, and not copying the reference makes sense because cloning is shallow. Could go either way. But the current stance is that cloning preserves references. > When an object is cloned, PHP will perform a shallow copy of all of the object's > properties. Any properties > that are references to other variables will remain references. https://www.php.net/manual/en/language.oop5.cloning.php Previous Comments: ------------------------------------------------------------------------ [2020-03-13 01:52:37] mvorisek at mvorisek dot cz Is the statement about cloning documented and desired? Outside cloning this approach makes sense and can not be even noticed, but shouln't clone create a (lazy - standard copy-on-write) copy of each scalar/array property no matter if this property was referenced or not? ------------------------------------------------------------------------ [2020-03-13 01:38:35] requinix@php.net Regarding the code from your email, https://3v4l.org/Q557K References are not pointers. > $test = &$x->elements; $test will not "point" to $x->elements. It will not be a reference "to" that property. Rather, this reference assignment will make it so that both of those symbols use the same data that is being stored internally by the engine. They are *both* references. Then when PHP clones the object, the property will be copied - including the fact that it is a reference (thus resulting in a *third* reference). See https://www.php.net/manual/en/language.references.php As a rule of thumb, whatever the problem may be, using references is *not* the solution. ------------------------------------------------------------------------ [2020-03-13 00:59:13] requinix@php.net You made the property a reference. PHP quite happily cloned the reference. ------------------------------------------------------------------------ [2020-03-13 00:57:32] mvorisek at mvorisek dot cz Description: ------------ Seems like a core bug presented in all PHP versions (5.4.0 - 7.4.3 tested). Please verify and fix asap. Test script: --------------- class A { public $elements = []; public function __construct() { $this->fields = &$this->elements; // this causes the issue } public function __clone() { // $elems = $this->elements; unset($this->elements); $this->elements = $elems; $this->fields = &$this->elements; // this is an immediate fix before fixed in PHP directly } } $x = new A(); $y = clone $x; $y->elements['hello'] = 'world'; print_r($x); print_r($y); Expected result: ---------------- A Object ( [elements] => Array ( ) [fields] => Array ( ) ) A Object ( [elements] => Array ( [hello] => world ) [fields] => Array ( [hello] => world ) ) Actual result: -------------- A Object ( [elements] => Array ( [hello] => world ) [fields] => Array ( [hello] => world ) ) A Object ( [elements] => Array ( [hello] => world ) [fields] => Array ( [hello] => world ) ) ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=79377&edit=1