class singleton {
 	private static $instance = null;
	private function singleton() { }
	public static function &getInstance() {
		if(is_null(self::$instance)) self::$instance = new self();
		return self::$instance;
	}
	public function __destruct() { }
	public function __clone() {
		trigger_error('Cloning instances of this class is forbidden.', E_USER_ERROR);
	}
	public function __wakeup() {
		trigger_error('Unserializing instances of this class is forbidden.', E_USER_ERROR);
	}
 }