how to split a string into an array containing all the characters of the string

[marcnyc]

Hello.
I am trying to find a way to split a string into characters but I don't know how to achieve this... explode() needs a separator, which doesn't apply in my case...
Basically I have:
$string = 'test';
and I'd like to find a way to be able to get this:
$array['0'] = 't';
$array['1'] = 'e';
$array['2'] = 's';
$array['3'] = 't';

Any ideas on how to do this? Is it even possible?