public function each(Closure $callback)
    {
        if (!is_callable($callback)) {
            return;
        }
        $data = [];
        $this->items ? $data = &$this->items : (!$this->data ?: $data = &$this->data);
        foreach ($data as $k => $v) {
            call_user_func_array($callback, [$k, $v]);
        }
    }