iterator.h

#ifndef _ITERATOR_H_
#define _ITERATOR_H_
#include <cstddef>
namespace EasySTL {
	//五种迭代器
	struct input_iterator_tag{};
	struct output_iterator_tag{};
	struct forward_iterator_tag : public input_iterator_tag {};
	struct bidirectional_iterator_tag : public forward_iterator_tag {};
	struct random_access_iterator_tag : public bidirectional_iterator_tag {};
    
    template<class T, class Distance>
    struct input_iterator {
       typedef input_iterator_tag iterator_category;
       typedef T                  value_type;
       typedef Distance           difference_type;
       typedef T*                 pointer;
       typedef T&                 reference;
    };
    
    template <class T, class Distance>
    struct output_iterator {
		typedef output_iterator_tag iterator_category;
		typedef void                value_type;
		typedef void                difference_type;
		typedef void                pointer;
		typedef void                reference;
	};

	template <class T, class Distance> 
	struct forward_iterator {
		typedef forward_iterator_tag	iterator_category;
		typedef T						value_type;
		typedef Distance				difference_type;
		typedef T*						pointer;
		typedef T&						reference;
	};

	template <class T, class Distance> 
	struct bidirectional_iterator {
		typedef bidirectional_iterator_tag	iterator_category;
		typedef T							value_type;
		typedef Distance					difference_type;
		typedef T*							pointer;
		typedef T&							reference;
	};
	template <class T, class Distance> 
	struct random_access_iterator {
		typedef random_access_iterator_tag	iterator_category;
		typedef T							value_type;
		typedef Distance					difference_type;
		typedef T*							pointer;
		typedef T&							reference;
	};

    //为避免挂一漏百，自行开发的迭代器最好继承自以下这个std::iterator
	template<class Category, class T, class Distance = ptrdiff_t,
	class Pointer = T*, class Reference = T&>
	struct iterator {
		typedef Category	iterator_category;
		typedef T			value_type;
		typedef Distance	difference_type;
		typedef Pointer		pointer;
		typedef Reference	reference;
	};
    
    //“榨汁机” traits
    template<class Iterator>
	struct iterator_traits {
		typedef typename Iterator::iterator_category	iterator_category;
		typedef typename Iterator::value_type			value_type;
		typedef typename Iterator::difference_type		difference_type;
		typedef typename Iterator::pointer				pointer;
		typedef typename Iterator::reference 			reference;
	};
    
    //针对原生指针而设计的traits偏特化
    template<class T>
	struct iterator_traits<T*> {
		typedef random_access_iterator_tag 	iterator_category;
		typedef T 							value_type;
		typedef ptrdiff_t 					difference_type;
		typedef T*							pointer;
		typedef T& 							reference;
	};
    
    //pointer to const 的特化版本
    template<class T>
	struct iterator_traits<const T*> {
		typedef random_access_iterator_tag 	iterator_category;
		typedef T 							value_type;
		typedef ptrdiff_t 					difference_type;
		typedef const T*					pointer;
		typedef const T& 					reference;
	};
    
    //判断ieterator的类型
    template<class Iterator>
    inline typename iterator_traits<Iterator>::iterator_category
      iterator_category(const Iterator& It) {
      	typedef typename iterator_traits<Iterator>::iterator_category category;
      	return category();
      }
    
    //获取迭代器的value_type
    template<class Iterator>
    inline typename iterator_traits<Iterator>::value_type*
      value_type(const Iterator& It) {
      	return static_cast<typename iterator_traits<Iterator>::value_type*>(0);
      }
    
    //获取迭代器的distance_type
    template<class Iterator>
	inline typename iterator_traits<Iterator>::difference_type*
	  difference_type(const Iterator& It){
		return static_cast<typename iterator_traits<Iterator>::difference_type*>(0);
	  }

}

#endif