map_iterator.hpp

#pragma once

#include <map>
#include <iterator>

template <typename Iter>
class map_iterator : public std::iterator<std::bidirectional_iterator_tag,
                                          typename Iter::value_type::second_type> {
public:
    using value_type = typename Iter::value_type::second_type;
    using iterator   = typename std::iterator<std::bidirectional_iterator_tag, value_type>;
    using reference  = typename iterator::reference;
    using pointer    = typename iterator::pointer;

    map_iterator() {}
    map_iterator(Iter j) : i(j) {}
    map_iterator& operator++() { ++i; return *this; }
    map_iterator operator++(int) { auto tmp = *this; ++(*this); return tmp; }
    map_iterator& operator--() { --i; return *this; }
    map_iterator operator--(int) { auto tmp = *this; --(*this); return tmp; }
    bool operator==(map_iterator j) const { return i == j.i; }
    bool operator!=(map_iterator j) const { return !(*this == j); }
    reference operator*() { return i->second; }
    pointer operator->() { return &i->second; }

protected:
    Iter i;
};

template <typename Iter>
inline map_iterator<Iter> make_map_iterator(Iter j) { return map_iterator<Iter>(j); }