public function get($key, $default = null, $separator = '.')
    {
        $key = array_filter(explode($separator, $key));
        $tmp = $this->data;
        foreach ($key as $k) {
            if (!isset($tmp[$k])) {
                return $default;
            }
            $tmp = $tmp[$k];
        }
        return $tmp;
    }