public static function &db($pdo = null)
    {
        $shared = self::instanced();
        if (is_object($pdo)) {
            $shared->dbLink = &$pdo;
        }
        if (!is_object($shared->dbLink)) {
            $shared->dbLink = self::db(SQL\PDO::singleton(is_array($pdo) ? $pdo : [
                ]));
        }

        return $shared->dbLink;
    }