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

Question

I realise the second one avoids the overhead of a function call (update, is actually a language construct), but it would be interesting to know if one is be

Answer 1

It makes a difference with array elements.

Consider this example

$a = array('test' => 1);
$a['test'] = NULL;
echo "Key test ", array_key_exists('test', $a)? "exists": "does not exist";

Here, the key 'test' still exists. However, in this example

$a = array('test' => 1);
unset($a['test']);
echo "Key test ", array_key_exists('test', $a)? "exists": "does not exist";

the key no longer exists.