Question

array_key_exists($name, $defaults)

isset($defaults[$name])

Answer 1

Yes, there is a difference. isset returns false if the value is null while array_key_exists doesn’t:

$defaults = array('foobar' => null);
var_dump(array_key_exists('foobar', $defaults));  // bool(true)
var_dump(isset($defaults['foobar']));             // bool(false)

So you should always use array_key_exists for array keys unless you don’t want to make a difference whether an array item exists or is null.