Method ~Queue

practice/itemPool.cpp:12–22

        _front = _rear = new QueueItem();
    }
    ~Queue()
    {
        QueueItem *cur = _front;
        while (cur != nullptr)
        {
            _front = _front->_next;
            delete cur;
            cur = _front;
        }

    }

    void push(const T &val) // 入队操作
    {