Doc #55164 [Ana]: Unclear/incorrect description of "casting to null"

Edit report at https://bugs.php.net/bug.php?id=55164&edit=1 ID: 55164 Updated by: frozenfire@php.net Reported by: deceze at gmail dot com Summary: Unclear/incorrect description of "casting to null" Status: Analyzed Type: Documentation Problem Package: Documentation problem PHP Version: Irrelevant Block user comment: N Private report: N New Comment: Rather, it seems that the confusion here is with what (unset) casting does. It's not meant to unset a variable, but rather to cast it to null. That casting type exists purely for completeness, and you may as well just use NULL. The way to undefine a variable is through the language construct unset. Perhaps I'll make a note in the unset() function reference that it's unrelated to unset- casting, and remove that errant example. Previous Comments: ------------------------------------------------------------------------ [2012-01-12 04:21:45] frozenfire at thefrozenfire dot com I believe the major distinction between the various states of the variable has to do not with the value, but rather its presence in the symbol table. When you assign null to a variable, it is still in the symbol table. When you cast it to unset, it's still in the symbol table until the operation finishes. When you unset it, it's removed from the symbol table, thus becoming "undefined". I'll see about confirming my suspicions through inspection of the source. ------------------------------------------------------------------------ [2011-07-08 21:53:07] deceze at gmail dot com Yes, but: error_reporting(E_ALL); var_dump($undefined); $foo = 'bar'; $foo = (unset)$foo; // or $foo = null var_dump($foo); unset($foo); var_dump($foo); Outputs: Notice: Undefined variable: undefined NULL NULL Notice: Undefined variable: foo NULL null is the default value for undefined variables, but undefined/"removed" variables are not the same as variables with a null value. ------------------------------------------------------------------------ [2011-07-08 21:47:26] philip@php.net Simply this: <?php var_dump($undefined); ?> Outputs NULL. ------------------------------------------------------------------------ [2011-07-08 21:40:14] deceze at gmail dot com $b = (unset)$a in itself is quite weird, since it doesn't unset either $a or $b, it just assigns null to $b. ------------------------------------------------------------------------ [2011-07-08 21:35:45] philip@php.net I agree there is a bug here, but you can cast something to null using (unset) so: $a = "foo"; $b = "bar"; $b = (unset) $a; var_dump($b); NULL Slightly odd that it's (unset) and not (null) but it is what it is. That section should refer to the (unset) documentation within the type juggling documentation. ------------------------------------------------------------------------ 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=55164 -- Edit this bug report at https://bugs.php.net/bug.php?id=55164&edit=1