C++ STL反向迭代器的实现

	template <class Iterator, class Ref, class Ptr>
	class reverse_iterator
	{
		typedef reverse_iterator<Iterator, Ref, Ptr> self;
	public:
	// 重载运算符函数
	private:
		Iterator _it;
	};

		Ref operator*()
		{
			//正常思路
			//return *_it;
			// 源码思路
			Iterator prev = _it;
			return *--prev;
		}

	// Iterator是哪个容器的迭代器，reverse_iterator<Iterator>就可以
	// 适配出哪个容器的反向迭代器。复用的体现
	template <class Iterator, class Ref, class Ptr>
	class reverse_iterator
	{
		typedef reverse_iterator<Iterator, Ref, Ptr> self;
	public:
		reverse_iterator(Iterator it)
			:_it(it)
		{}

		Ref operator*()
		{
			//正常思路
			//return *_it;
			Iterator prev = _it;
			return *--prev;
		}

		Ptr operator->()
		{
			return &operator*();
		}

		self& operator++()
		{
			--_it;
			return *this;
		}

		self& operator--()
		{
			++_it;
			return *this;
		}

		bool operator!= (const self& rit) 
		{
			return _it != rit._it;
		}

	private:
		Iterator _it;// 封装任何类型的正向迭代器
	};

	// iterator -> 类去分装节点指针，重载*、++ 等运算符，让它们像指针一样使用
	template<class T,class Ref,class Ptr>
	class _list_iterator
	{
	public:
		typedef _list_iterator < T, Ref,Ptr> self;
		typedef Listnode<T> Node;
		_list_iterator( Node* x)
			:_node(x)
		{}
		// ++it
		self& operator++()
		{
			_node = _node->_next;
			return *this;
		}

		// it++
		self operator++(int)
		{
			self tmp(*this);
			_node = _node->_next;
			return tmp;
		}

		// --it
		self& operator--()
		{
			_node = _node->_pre;
			return *this;
		}

		// it--
		self operator--(int)
		{
			self tmp(*this);
			_node = _node->_pre;
			return tmp;
		}

		//*
		Ref operator*()
		{
			return _node->_data;
		}
		//->
		Ptr operator->()
		{
			return &(_node->_data);
		}
		//!=
		bool operator!=(const self& x)
		{
			return _node != x._node;
		}
		//==
		bool operator==(const self& x)
		{
			return _node == x._node;
		}

		Node* _node;
	};

template<class T>
	class list
	{
	public:
		typedef ListNode<T> Node;
		typedef _list_iterator<T, T&, T*> iterator;
		typedef _list_iterator<T, const T&, const T*> const_iterator;
		typedef reverse_iterator<const_iterator, const T&, const T*> const_reverse_iterator;
		typedef reverse_iterator<iterator, T&, T*> reverse_iterator;
		reverse_iterator rbegin()
		{
			return reverse_iterator(end());
		}
		const_reverse_iterator rbegin()const
		{
			return const_reverse_iterator(end());
		}
		reverse_iterator rend()
		{
			return reverse_iterator(begin());
		}
		const_reverse_iterator rend()const
		{
			return const_reverse_iterator(begin());
		}
		iterator begin()
		{
			return iterator(_head->_next);
		}
		iterator end()
		{
			return iterator(_head);
		}
		const_iterator begin()const
		{
			return const_iterator(_head->_next);
		}
		const_iterator end()const
		{
			return const_iterator(_head);
		}
		list()
		{
			_head= new Node();
			_head->_next = _head;
			_head->_pre = _head;
		}
		

		void push_back(const T&x)
		{
			Node* newnode = new Node(x);
			Node* tail = _head->_pre;
			newnode-> _pre = tail;
			tail->_next = newnode;
			newnode->_next = _head;
			_head->_pre = newnode;
		}

	private:
		Node* _head;// 头结点指针
	};

	void test11()
	{
		BBQ::list<int> L1;
		L1.push_back(1);
		L1.push_back(2);
		L1.push_back(3);
		reverse_print_list(L1);
	}