final public static function setInstance($instance)
    {
        if ($instance instanceof PDO) {
            $instance = $instance->getAttribute(PDO::ATTR_DRIVER_NAME);
        }
        if (is_string($instance)) {
            if (class_exists('SQL\Writer\\' . $instance)) {
                $class = 'SQL\Writer\\' . $instance ;
                $instance = new $class;
            } else {
                $instance = new self;
            }
        }

        if (!($instance instanceof self)) {
            throw new RuntimeException('$instance must an instanceof SQL\Writer');
        }

        self::$instance = $instance;
    }