#32841 [Asn->WFx]: returned a member variable cannot be turned into reference

ID: 32841 Updated by: alan_k@php.net Reported By: wagner at bonn dot edu -Status: Assigned +Status: Wont fix Bug Type: Scripting Engine problem Operating System: * PHP Version: 4.3.11, 5.0.4 Assigned To: andi New Comment: What you are trying to do is feasable in different ways. - just not the way you are trying.. (try the support channels for suggestions.) - whether what you are trying to do is a good idea (maintance, code readability, creating bugs....) is another question... changing the engine behavior to do what you say is extremely complex. And the return on fixing this would not be worth the instability that it would involve (we know from previous efforts at looking at this). hint: use return &$this->var; $tmp = &$foo->f_default(); incr($tmp); Previous Comments: ------------------------------------------------------------------------ [2005-04-28 06:34:50] wagner at bonn dot edu > In your case f_default() returns *copy*, not a reference No it doesn't. Try this as case 1 in the reproduce code as above: -------------------------------------------------- case 1: //forced reference works AND makes default behaviour //work afterwards echo incr($foo->f_ref())."\n"; echo incr($foo->f_default())."\n"; echo incr($foo->f_default())."\n"; break; Expected result: ---------------- 1 2 2 f_default() should return a copy Actual result: -------------- 1 2 3 incr() gets a reference to $foo->v and modifies it Since I filed this behaviour as another bug here http://bugs.php.net/bug.php?id=32840 could it please be looked at too and be unbogusified? ------------------------------------------------------------------------ [2005-04-27 23:45:04] tony2001@php.net Short version: this is expected and the error message clearly says why: only variables can be referenced and you cannot make a reference to an expression result. Long version: In your case f_default() returns *copy*, not a reference as you wrongly consider, while f_ref() returns reference and should work indeed. But I'm a bit surprised to see that f_copy() works, as it should give the same warning as with f_default(). Concerning the case 2, AFAIK it's because of some reference magic: when you return $this->v as reference, it turns in refernce itself (refcount++) and the following call to f_default() returns this reference. Though, it would be interesting to see what engine gurus say about it. ------------------------------------------------------------------------ [2005-04-26 14:54:41] wagner at bonn dot edu Description: ------------ When returning a member-variable directly as a reference parameter into a function, a fatal error occurs: Fatal error: Only variables can be passed by reference ... The reproduce code displays the bug (for $case=0) as well as two simple workarounds that IMHO show that the ZEND-Engine should be able to handle this with no need for any error. This seems to have been around for a while, at least PHP 4.3.x Probably related to http://bugs.php.net/bug.php?id=32840 Reproduce code: --------------- $case = 0; function incr(&$int) { return $int++; } class foo { var $v = 1; function &f_ref() { return $this->v; } function f_copy() { return (int)$this->v; } //forced copy through type-cast function f_default() { return $this->v; } } $foo =& new foo(); switch($case) { case 0: //default behaviour is broken echo incr($foo->f_default())."\n"; case 1: //forced reference works AND makes default behaviour work afterwards echo incr($foo->f_ref())."\n"; echo incr($foo->f_default())."\n"; break; case 2: //forced copy works echo incr($foo->f_copy())."\n"; break; } Expected result: ---------------- incr() should get a copy of $foo->v Actual result: -------------- Fatal error: Only variables can be passed by reference in foo.php on line 19 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=32841&edit=1