iterator

• 구현
  https://www.cplusplus.com/reference/iterator/iterator/?kw=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;
	};

별로 설명할게없음.
std::ptrdiff_t 도 따로했고, category도 정리해둠.
어쨋든, iterator 구조체는 나중에, reverse_iterator에서 사용됨.

https://wetodev.rd.tuni.fi/wetoextra/cpp/en/cpp/iterator/reverse_iterator.html

template< class Iterator >
class reverse_iterator : public std::iterator<
                           typename std::iterator_traits<Iterator>::iterator_category,
                           typename std::iterator_traits<Iterator>::value_type,
                           typename std::iterator_traits<Iterator>::difference_type,
                           typename std::iterator_traits<Iterator>::pointer,
                           typename std::iterator_traits<Iterator>::reference >

iterator_traits

반복자와 배열의 포인터를 구분하기위해서 만들어진것!

• 구현

template<class Iter>
struct iterator_traits {
	public:
		typedef typename Iter::iterator_category	terator_category;
		typedef typename Iter::difference_type		difference_type;
		typedef typename Iter::value_type			value_type;
		typedef typename Iter::pointer				pointer;
		typedef typename Iter::reference			reference;
};

// iterator traits for pointer
/*
int main()
{
	typedef std::iterator_traits<int*> traits;
	if (typeid(traits::iterator_category)==typeid(std::random_access_iterator_tag))
		 std::cout << "int* is a random-access iterator";
	return 0;
}
*/

// container를 위한 iterator_traits
template<class T>
struct iterator_traits<T *>
{
	typedef random_access_iterator_tag	iterator_category;
	typedef T value_type;
	typedef ptrdiff_t difference_type;
	typedef ptrdiff_t distance_type;
	typedef T *pointer;
	typedef T &reference;
};

// iterator traits for const pointer
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 ptrdiff_t distance_type;
	typedef T *pointer;
	typedef T &reference;
};