I remember that there were function that have such functionality. Unfortunately, I don't remember the name of it. Basically, it did something like...
$values = foo(array('x', 'y', 'z'), $_POST);
If there are such keys in the array, it does return new array (named $values) with only those keys... taken from $_POST. If one or more keys aren't in $_POST, it simply returns false.
Anyone remember something like that or I was just dreaming? Thanks in advice!