map_iter: (broken) map iterator in C++.

map_iter.hpp

template<class InputIt>
using value_type = typename std::iterator_traits<InputIt>::value_type;

template<class InputIt>
using iterator_category = typename std::iterator_traits<InputIt>::iterator_category;

template<class InputIt>
using difference_type = typename std::iterator_traits<InputIt>::difference_type;

template<class InputIt>
using pointer = typename std::iterator_traits<InputIt>::pointer;

template<class InputIt>
using reference = typename std::iterator_traits<InputIt>::reference;

template<class IterType, class Fun>
class map_iter:
  public std::iterator<iterator_category<IterType>,
  value_type<IterType>,
  difference_type<IterType>,
  pointer<IterType>,
  reference<IterType>>
  {
    IterType iter;
    Fun fun;
    explicit map_iter(IterType _iter): iter(_iter), fun([](){}) {}
    explicit map_iter(IterType _iter, Fun f): iter(_iter), fun(f) {}
    map_iter& operator++() { ++iter; return *this; }
    map_iter operator++(int) { map_iter prev = *this; ++iter; return prev; }
    bool operator==(map_iter other) const { return iter == other.iter; }
    bool operator!=(map_iter other) const { return iter != other.iter; }
    bool operator==(IterType other) const { return iter == other; }
    bool operator!=(IterType other) const { return iter != other; }
    reference<IterType> operator*() const { return fun(*iter); }
  };