Required __construct call in SplFileObject

Hi, I'm just curious is there a reason why SplFileObject requires a call to parent::__construct() if I override the class? Someone on my twitter feed mentioned it because he tried to create a Mock-Object. The following code gives me: PHP Fatal error: Uncaught exception 'LogicException' with message 'The parent constructor was not called: the object is in an invalid state <?php class cls1 extends \SplFileObject {

            public function __construct()
            {

            }

            public function fpassthru()
            {
            }

} $cl = new cls1(); $cl->fpassthru();