9 Iterators library [iterators]

9.7.1.1 Class template reverse_iterator [reverse.iterator]

namespace std { namespace experimental { namespace ranges { inline namespace v1 {
  template <BidirectionalIterator I>
  class reverse_iterator {
  public:
    using iterator_type = I;
    using difference_type = difference_type_t<I>;
    using value_type = value_type_t<I>;
    using iterator_category = iterator_category_t<I>;
    using reference = reference_t<I>;
    using pointer = I;

    constexpr reverse_iterator();
    explicit constexpr reverse_iterator(I x);
    constexpr reverse_iterator(const reverse_iterator<ConvertibleTo<I>>& i);
    constexpr reverse_iterator& operator=(const reverse_iterator<ConvertibleTo<I>>& i);

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

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

    constexpr reverse_iterator  operator+ (difference_type n) const
      requires RandomAccessIterator<I>;
    constexpr reverse_iterator& operator+=(difference_type n)
      requires RandomAccessIterator<I>;
    constexpr reverse_iterator  operator- (difference_type n) const
      requires RandomAccessIterator<I>;
    constexpr reverse_iterator& operator-=(difference_type n)
      requires RandomAccessIterator<I>;
    constexpr reference operator[](difference_type n) const
      requires RandomAccessIterator<I>;

    friend constexpr rvalue_reference_t<I> iter_move(const reverse_iterator& i)
      noexcept(see below);
    template <IndirectlySwappable<I> I2>
      friend constexpr void iter_swap(const reverse_iterator& x, const reverse_iterator<I2>& y)
        noexcept(see below);

  private:
    I current; // exposition only
  };

  template <class I1, class I2>
      requires EqualityComparableWith<I1, I2>
    constexpr bool operator==(
      const reverse_iterator<I1>& x,
      const reverse_iterator<I2>& y);
  template <class I1, class I2>
      requires EqualityComparableWith<I1, I2>
    constexpr bool operator!=(
      const reverse_iterator<I1>& x,
      const reverse_iterator<I2>& y);
  template <class I1, class I2>
      requires StrictTotallyOrderedWith<I1, I2>
    constexpr bool operator<(
      const reverse_iterator<I1>& x,
      const reverse_iterator<I2>& y);
  template <class I1, class I2>
      requires StrictTotallyOrderedWith<I1, I2>
    constexpr bool operator>(
      const reverse_iterator<I1>& x,
      const reverse_iterator<I2>& y);
  template <class I1, class I2>
      requires StrictTotallyOrderedWith<I1, I2>
    constexpr bool operator>=(
      const reverse_iterator<I1>& x,
      const reverse_iterator<I2>& y);
  template <class I1, class I2>
      requires StrictTotallyOrderedWith<I1, I2>
    constexpr bool operator<=(
      const reverse_iterator<I1>& x,
      const reverse_iterator<I2>& y);
  template <class I1, class I2>
      requires SizedSentinel<I1, I2>
    constexpr difference_type_t<I2> operator-(
      const reverse_iterator<I1>& x,
      const reverse_iterator<I2>& y);
  template <RandomAccessIterator I>
    constexpr reverse_iterator<I> operator+(
      difference_type_t<I> n,
      const reverse_iterator<I>& x);

  template <BidirectionalIterator I>
    constexpr reverse_iterator<I> make_reverse_iterator(I i);
}}}}