php - what's the benefit of unsetting variables? [duplicate]

Question

Possible Duplicates:
What's better at freeing memory with PHP: unset() or $var = null

Is there a real benefit of unsetting variables in php?

class test {    public function m1($a, $b)     $c = $a + $b;     unset($a, $b);     return $c;   } } 

Is it true that unsetting variables doesn't actually decrease the memory consumption during runtime?

Answer 1

Is it true that unsetting variables doesn't actually decrease the memory consumption during runtime?

Yep. From PHP.net:

unset() does just what it's name says - unset a variable. It does not force immediate memory freeing. PHP's garbage collector will do it when it see fits - by intention as soon, as those CPU cycles aren't needed anyway, or as late as before the script would run out of memory, whatever occurs first.

If you are doing $whatever = null; then you are rewriting variable's data. You might get memory freed / shrunk faster, but it may steal CPU cycles from the code that truly needs them sooner, resulting in a longer overall execution time.

Regarding your other question:

And is there any reason to unset variables apart from destroying session varaibles for instance or for scoping?

Not really, you pretty much summed it.