27 Iterators library [iterators]

namespace std {
  template <class Iterator>
  class move_iterator {
  public:
    using iterator_type     = Iterator;
    using iterator_category = typename iterator_traits<Iterator>::iterator_category;
    using value_type        = typename iterator_traits<Iterator>::value_type;
    using difference_type   = typename iterator_traits<Iterator>::difference_type;
    using pointer           = Iterator;
    using reference         = see below;

    constexpr move_iterator();
    constexpr explicit move_iterator(Iterator i);
    template <class U> constexpr move_iterator(const move_iterator<U>& u);
    template <class U> constexpr move_iterator& operator=(const move_iterator<U>& u);

    constexpr iterator_type base() const;
    constexpr reference operator*() const;
    constexpr pointer operator->() const;

    constexpr move_iterator& operator++();
    constexpr move_iterator operator++(int);
    constexpr move_iterator& operator--();
    constexpr move_iterator operator--(int);

    constexpr move_iterator operator+(difference_type n) const;
    constexpr move_iterator& operator+=(difference_type n);
    constexpr move_iterator operator-(difference_type n) const;
    constexpr move_iterator& operator-=(difference_type n);
    constexpr unspecified operator[](difference_type n) const;

  private:
    Iterator current;   // exposition only
  };

  template <class Iterator1, class Iterator2>
    constexpr bool operator==(
      const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
  template <class Iterator1, class Iterator2>
    constexpr bool operator!=(
      const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
  template <class Iterator1, class Iterator2>
    constexpr bool operator<(
      const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
  template <class Iterator1, class Iterator2>
    constexpr bool operator<=(
      const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
  template <class Iterator1, class Iterator2>
    constexpr bool operator>(
      const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
  template <class Iterator1, class Iterator2>
    constexpr bool operator>=(
      const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);

  template <class Iterator1, class Iterator2>
    constexpr auto operator-(
      const move_iterator<Iterator1>& x,
      const move_iterator<Iterator2>& y) -> decltype(x.base() - y.base());
  template <class Iterator>
    constexpr move_iterator<Iterator> operator+(
      typename move_iterator<Iterator>::difference_type n, const move_iterator<Iterator>& x);
  template <class Iterator>
    constexpr move_iterator<Iterator> make_move_iterator(Iterator i);
}