Bug #74020 [Ver->Csd]: Foreach-by-reference + assignment may recreate unexpected key references

Edit report at https://bugs.php.net/bug.php?id=74020&edit=1 ID: 74020 Updated by: requinix@php.net Reported by: icarpenter at leadid dot com Summary: Foreach-by-reference + assignment may recreate unexpected key references -Status: Verified +Status: Closed Type: Bug Package: Scripting Engine problem PHP Version: 7.0.15 -Assigned To: +Assigned To: requinix Block user comment: N Private report: N New Comment: They're both references to the same thing, because > I'd expect $item to be a reference to the last array item after the first loop that's not what is actually happening. A reference is not technically to another variable but to a shared value in memory. $item does not "point" to the last item in the array, rather it and the array item both use the same shared value. Thus why they are both references. unset()ing $item destroys one of the two references, and since there's only one left it does not need to be a reference anymore. Closing because as far as I know the originally-reported bug only affects PHP 7.0 and that is no longer supported. Previous Comments: ------------------------------------------------------------------------ [2019-02-17 12:29:06] glueball at gmail dot com I've found another instance of this same issue (I think it's the same): https://3v4l.org/oe98G While it's true that it gets fixed easily by unsetting the variable after the loop, this behavior is very unexpected, and does not seem right. I'd expect $item to be a reference to the last array item after the first loop, but apparently the last item in the array is also a reference to "something" (as can be seen by the "&" sign in the intermediate var_dump) ------------------------------------------------------------------------ [2018-10-23 22:59:41] fra dot martin at free dot fr Previous comment was supposed to end at «...Sorry for my previous useless comment.» ------------------------------------------------------------------------ [2018-10-23 22:54:05] fra dot martin at free dot fr I know what a reference is... But you are right, my expectation is false. Indeed I did not take time to understand step by step what happened here: - the first foreach leaves $item referencing the last array's element - the second foreach loop assigns successively $item with the 1st value (which also modifies the last element since $item is a pointer on it, its value is now 1), then the 2nd one (which re-assigns $item and the last element, its value becomes 2), then the 3rd one, which re-assings $item and itself with its current value '2'. Sorry for my previous useless comment. In my previous example, the first foreach loop creates a reference variable and makes it reference successively the 1st, 2nd and 3rd element in the array. After the first foreach loop, I understand that $item still references the last array's element (int(3)), that's what would give a 'var_dump($item);' The second foreach loop uses the same variable (still a reference since created as such in the first foreach loop) and iterates over each element, assigning ------------------------------------------------------------------------ [2018-10-23 21:30:34] spam2 at rhsoft dot net your expectation is imply wrong foreach($items as &$item); unset($item); foreach($items as $item); you miss the unset! either understand what references are or don't use them ------------------------------------------------------------------------ [2018-10-23 20:25:16] fra dot martin at free dot fr This is probably the same issue, much more direct and very disturbing for me. These two simple foreach loops do nothing, they just use the same variable name, once by reference, once by value: the last array element always becomes a copy of the penultimate element! $items = [1,2,3]; foreach($items as &$item); foreach($items as $item); echo array_pop($items); Expected result: 3 Actual result: 2 Expected result: ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=74020 -- Edit this bug report at https://bugs.php.net/bug.php?id=74020&edit=1