private static function isRegistered($isClass, $class, $method, $autoloader = null)
    {
        // get autoloader if not received via parameter
        if (!$autoloader) {
            $autoloader = self::getSplAutoloader();
        }

        // construct lookup-string
        if ($isClass) {
            $needle = array($class, $method);
        } else {
            $needle = $method;
        }

        // return status
        return in_array($needle, $autoloader);
    }