模拟实现list容器

要模拟实现c++stl的list容器，首先得知道它是双向带头循环列表，就像下面这张图一样

老样子，由于迭代器部分的实现需要绕一下脑子，并且和之前vector的模拟实现中的迭代器设计方式不一样，因此我单独把迭代器部分的设计拿出来

由于正向迭代器和反向迭代器的++和--的方向不一致，因此单独设计出正向迭代器和反向迭代器

---

正向迭代器

	
	template<class T, class Ref, class Ptr>
	struct _list_iterator
	{
		typedef list_node<T> Node;
		typedef _list_iterator<T, Ref, Ptr> self;

		Node* _node;

		_list_iterator(Node* node)
			:_node(node)
		{}

		Ref operator*() const
		{
			return _node->_val;
		}

		self& operator++()
		{
			_node = _node->_next;
			return *this;
		}
		self operator++(int x)
		{
			self tmp(*this);
			_node = _node->_next;
			return tmp;
		}
		self& operator--()
		{
			_node = _node->_prev;
			return *this;
		}
		self operator--(int x)
		{
			self tmp(*this);
			_node = _node->_prev;
			return tmp;
		}

		bool operator==(const self& it) const
		{
			return _node == it._node;
		}
		bool operator!=(const self& it) const
		{
			return _node != it._node;
		}
		Ptr operator->() const
		{
			return &(operator*());
		}
	};

反向迭代器的设计

template<class Iterator, class Ref, class Ptr>
struct Reverse_Iterator
{
	typedef Reverse_Iterator<Iterator, Ref, Ptr> self;
	Iterator _it;
	
	Reverse_Iterator(Iterator it)
		:_it(it)
	{}
	Ref operator*() const
	{
		Iterator tmp = _it;
		return *(--tmp);
	}
	Ptr operator->()
	{
		return &(operator*());
	}
	self& operator++()
	{
		--_it;
		return *this;
	}
	self& operator--()
	{
		++_it;
		return *this;
	}
	self operator++(int)
	{
		self tmp = *this;
		--_it;
		return tmp;
	}
	self operator--(int)
	{
		self tmp = *this;
		++_it;
		return tmp;
	}
	bool operator!=(const self& s) const
	{
		return _it != s._it;
	}
};

其余部分

#pragma once
#include <iostream>
#include <assert.h>
using namespace std;

namespace wzn
{
	template<class T>
	struct list_node
	{
		list_node<T>* _next;
		list_node<T>* _prev;
		T _val;

		list_node(const T& val = T())
			:_next(nullptr)
			,_prev(nullptr)
			,_val(val)
		{}
	};


	template<class T>
	class list
	{
		typedef list_node<T> Node;
	public:
		//typedef _list_iterator<T> iterator;
		//typedef _list_iterator<T> const_iterator;
		typedef _list_iterator<T, T&, T*> iterator;
		typedef _list_iterator<T, const T&, const T*> const_iterator;

		typedef Reverse_Iterator<iterator, T&, T*> reverse_iterator;
		typedef Reverse_Iterator<const_iterator, const T&, const T*> const_reverse_iterator;

		void empyt_init()
		{
			_head = new Node;
			_head->_next = _head;
			_head->_prev = _head;
			_size = 0;
		}

		list()
		{
			// 库里的是带头双向循环链表，因此必须有个看门狗节点
			empyt_init();
		}
		list(const list<T>& lt)
		{
			empyt_init();
			for (auto& e : lt)
			{
				push_back(e);
			}
		}
		~list()
		{
			clear();
			delete _head;
			_head = nullptr;
		}

		void swap(list<T>& lt)
		{
			std::swap(_head, lt._head);
			std::swap(_size, lt._size);
		}
		// 这里的形参是list<T> lt而不是const list<T> lt，因为调用swap的话，后者的内容是不能修改的
		list<T>& operator=(list<T> lt)
		{
			swap(lt);
			return *this;
		}

		void clear()
		{
			iterator it = begin();
			while (it != end())
			{
				// erase会返回下一个节点的地址
				it = erase(it);
			}
			_size = 0;
		}

		iterator begin()
		{
			//return iterator(_head->_next);
			return _head->_next;	//隐式类型转换 + 匿名对象
		}
		iterator end()
		{
			//return iterator(_head);
			return _head;
		}
		const_iterator begin() const
		{
			//return iterator(_head->_next);
			return _head->_next;	//隐式类型转换 + 匿名对象
		}
		const_iterator end() const
		{
			//return iterator(_head);
			return _head;
		}

		reverse_iterator rbegin()
		{
			return end();
		}
		reverse_iterator rend()
		{
			return begin();
		}
		const_reverse_iterator rbegin() const
		{
			return end();
		}
		const_reverse_iterator rend() const
		{
			return begin();
		}

		void push_back(const T& val)
		{
			//Node* tail = _head->_prev;
			//Node* newnode = new Node(val);

			//tail->_next = newnode;
			//newnode->_prev = tail;
			//
			//newnode->_next = _head;
			//_head->_prev = newnode;
			insert(end(),val);
		}
		void push_front(const T& val)
		{
			insert(begin(), val);
		}
		
		void pop_back()
		{
			//Node* tail = _head->_prev;

			//tail->_prev->_next = _head;
			//_head->_prev = tail->_prev;

			//delete[] tail;
			//tail = nullptr;
			erase(--end());
		}

		void pop_front()
		{
			erase(begin());
		}

		iterator insert(iterator pos, const T& val)
		{
			Node* newnode = new Node(val);
			Node* cur = pos._node;
			Node* prev = cur->_prev;

			newnode->_prev = prev;
			prev->_next = newnode;

			newnode->_next = cur;
			cur->_prev = newnode;

			++_size;
			return newnode;
		}

		iterator erase(iterator pos)
		{
			assert(pos != end());

			Node* cur = pos._node;
			Node* prev = cur->_prev;
			Node* next = cur->_next;

			prev->_next = next;
			next->_prev = prev;

			delete cur;
			cur = nullptr;
			--_size;
			return next;
		}

		size_t size() const
		{
			return _size;
		}

	private:
		Node* _head;
		size_t _size = 0;
	
	};




}