Bug #75632 [Com]: Wrong behavior of clone and references

Edit report at https://bugs.php.net/bug.php?id=75632&edit=1 ID: 75632 Comment by: kripper at imatronix dot com Reported by: kripper at imatronix dot com Summary: Wrong behavior of clone and references Status: Not a bug Type: Bug Package: Scripting Engine problem Operating System: All PHP Version: 7.1.12 Block user comment: N Private report: N New Comment: Thanks for your time. I'm afraid that the posted code is not a solution for the general case. My previous comments were not quite clear so I wrote something more elaborated here: https://docs.google.com/document/d/11_uIZyvXzPBTv8-1id-xl9itYpJ4lGaSquWhEvmPgK4/edit#heading=h.lbjyy98sok62 Previous Comments: ------------------------------------------------------------------------ [2017-12-06 08:35:24] requinix@php.net That code is a bit weird so I'm going to make what I think are some corrections: $ref = $base->data['nodes']['subNodes']['subSubNodes']; foreach($ref as $key => $res) { if(!$res['sub']) $res['sub'] = 'something'; $res = CloneObjectsWithoutUnsettingRefs($res); if($res['other'] == 'ok') $res['ok'] = true; $ref[$key] = $res; } $base->data['nodes']['subNodes']['subSubNodes'] = $ref; Point is you can modify the copies and then overwrite the originals. ------------------------------------------------------------------------ [2017-12-05 21:39:41] kripper at imatronix dot com Thanks Damian, I want to write legible code like this: $ref = & $base->data['nodes']['subNodes']['subSubNodes']; foreach($res as &val) { if(!$res['sub']) $res['sub'] = 'something'; CloneObjectsWithoutUnsettingRefs($res); if($res['other'] = 'ok') $res['ok'] = true; } Instead of: foreach($base->data['nodes']['subNodes']['subSubNodes'] as &val) { if(!$base->data['nodes']['subNodes']['subSubNodes']['sub']) $base->data['nodes']['subNodes']['subSubNodes']['sub'] = 'something'; CloneObjectsWithoutUnsettingRefs($base->data['nodes']['subNodes']['subSubNodes']); if($base->data['nodes']['subNodes']['subSubNodes']['other'] = 'ok') $base->data['nodes']['subNodes']['subSubNodes']['ok'] = true; } What is the best approach for this? Using references causes problems when cloning objects. ------------------------------------------------------------------------ [2017-12-05 19:13:07] requinix@php.net > // But since PHP 7.1, ... > It seems like references are not really references anymore, They've always worked that way. https://3v4l.org/70ZIS > Of course, we can unset the reference before doing clone, but it's not feasible > cosidering we can accidently call clone from a subfunction while the reference is > still alive. > Is there any solution or workaround? Unsetting the reference before the function call is the answer. Not using a reference in the first place is an even better answer. Using a reference for legibility? I don't see how ChangeData($ref); is more understandable than ChangeData($base->data['nodes']['subNodes']); Using a reference for performance? Don't. That's the #1 way to abuse references. PHP is already efficient with variables and it already has copy-on-write functionality so don't fight it by trying to be clever. If you want to propose additions like pointers or changes like... I don't know what you want to change with references... then check out PHP's RFC process. https://wiki.php.net/rfc/howto ------------------------------------------------------------------------ [2017-12-05 18:51:12] kripper at imatronix dot com <?php // We used to have objects with multilevel array data... $base = new stdClass(); $base->data = array( 'nodes' => array( 'subNodes' => array( 'subSubNodes' => '...' ) ) ); // And we used references to write cleaner code: $ref = & $base->data['nodes']['subNodes']['subSubNodes']; // ChangeData($ref); // Instead of: // ChangeData($base->data['nodes']['subNodes']); // This has a very big impact on legibility, if not performance. // But since PHP 7.1, keeping references prevents 'clone' to work properly // because the cloned object properties are treated as references to the // original object properties. $clone = clone $base; // So, when changing the cloned object... $clone->data['nodes']['subNodes'] = 'Changed by clone'; // ...the original object is also modified (result is: 'Changed by clone'). die("Base object has property: " . $base->data['nodes']['subNodes']); It seems like references are not really references anymore, but variable aliases, which cannot be usted together with clone(). Actually, we feel references aren't safe nor usefull anymore, but for 'out arguments' when calling functions (which can better be done by returning arrays anyway). Of course, we can unset the reference before doing clone, but it's not feasible cosidering we can accidently call clone from a subfunction while the reference is still alive. Is there any solution or workaround? If not, we probably have a language design problem here that will make noise to serious developers until PHP introduces pointers or references that can be usted together with clone. ------------------------------------------------------------------------ [2017-12-05 14:55:16] requinix@php.net Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php References are not pointers: $ptr does not "point" to $orig->test, rather they both use the same underlying value stored in memory. Also, creating a reference forces both sides of the assignment to be references - otherwise the system wouldn't work. http://php.net/manual/en/language.references.php If you unset($ptr) before the clone then $orig->test will become the only reference to its value left and so automatically revert to a normal unreferenced value. https://3v4l.org/c6epk ------------------------------------------------------------------------ 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=75632 -- Edit this bug report at https://bugs.php.net/bug.php?id=75632&edit=1