#20842 [Opn]: No explanation of object comparison and copying

ID: 20842 Updated by: goba@php.net Reported By: dparks@verinform.com Status: Open Bug Type: Documentation problem Operating System: Any PHP Version: 4.2.3 New Comment: Jesus, it would be nice to have your examples in the documentation. I cannot add it right now, unfortunately. Previous Comments: ------------------------------------------------------------------------ [2002-12-05 19:53:03] dparks@verinform.com Argh!! Apparently, PHP evaluates $this->val = val; without error, treating val like 'val'. I can't find this documented in the manual. The code posted near the end of the bug at http://bugs.php.net/bug.php?id=20681 (look for [28 Nov 2:02pm] moriyoshi@php.net) contains an error like this, which was not noticed by 4 people. Because of this, the code returns true for all comparisons. The behavior you describe is what I expected. Sorry about the mixup. It would still be nice to have an explanation about how copies (assignment) are done on objects -- is this a deep value copy? How are references handled? Also, it would be nice if the comparison operator page explained how recursion is handled. ------------------------------------------------------------------------ [2002-12-05 19:11:48] jmcastagnetto@php.net Can you be more precise about what comparison operations you have in mind? Remember that PHP is not OOP, it is a language that supports OOP-style coding, so there is no inherent way of checking if 2 different instances of objects are of the same class w/ the same properties, or two variables pointing to the same object instance. The following code generates the expected result: function bool2str($bool) { if ($bool === false) { return 'FALSE'; } else { return 'TRUE'; } } class Foo { var $flag; function Foo($flag=true) { $this->flag = $flag; } } $o = new Foo(); $p = new Foo(false); $q = new Foo(); // this should be true echo bool2str($o == $q)."\n"; // this should be false echo bool2str($o != $q)."\n"; // this should be true echo bool2str($o === $q)."\n"; // this should be false echo bool2str($o == $p)."\n"; // this should be false echo bool2str($o === $p)."\n"; // this should be true echo bool2str($o != $p)."\n"; // this should be true echo bool2str($o !== $p)."\n"; ------------------------------------------------------------------------ [2002-12-05 16:22:03] dparks@verinform.com I cannot find any explanation of object copying or comparison in the PHP manual (or in the user comments). Even a note saying "don't expect comparison operators to work on objects" would by useful -- it would have saved me a couple of days of debugging and rewriting code. ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=20842&edit=1