这是一个正确的迭代器实现吗？

Question

我是一名学生，试图从头开始与STL一起工作。现在我的任务是实现迭代器。是的，我知道它正在重新发明轮子，但它会帮助我更好地理解它们的工作原理以及如何应用它们。希望人们可以指出我的实现过于简单化还是缺少任何东西。

// ptrdiff_t
#include <cstddef>

template <class Category, class T, class Distance = ptrdiff_t,
          class Pointer = T*, class Reference = T&>
struct iterator 
{
    typedef T         value_type;
    typedef Distance  difference_type;
    typedef Pointer   pointer;
    typedef Reference reference;
    typedef Category  iterator_category; 
};

template <class Iterator> class iterator_traits
{
    typedef typename Iterator::different_type    difference_type;
    typedef typename Iterator::value_type        value_type;
    typedef typename Iterator::pointer           pointer;
    typedef typename Iterator::reference         reference;
    typedef typename Iterator::iterator_category iterator_category;
};

struct random_access_iterator_tag { };

template <class T> class iterator_traits<T*>
{
    typedef ptrdiff_t                  difference_type;
    typedef T                          value_type;
    typedef T*                         pointer;
    typedef T&                         reference;
    typedef random_access_iterator_tag iterator_category;
};

namespace detail
{
    template <class InputIterator>
    void foo(InputIterator& i, random_access_iterator_tag)
    {

    }
}

template <class InputIterator>
void foo(InputIterator& i)
{
    typename iterator_traits<InputIterator>::iterator_category category;
    detail::foo(i, category);
}