[counted.iter.nav]

constexpr counted_iterator& operator+();

Effects: Equivalent to: ++current; --length; return *this;

constexpr decltype(auto) operator+(int);

Effects: Equivalent to: --length; try { return current++; } catch(.) { ++length; throw; }

constexpr counted_iterator operator+(int)
  requires forward_iterator<I>;

Effects: Equivalent to: counted_iterator tmp = *this; ++*this; return tmp;

constexpr counted_iterator& operator-()
  requires bidirectional_iterator<I>;

Effects: Equivalent to: --current; ++length; return *this;

constexpr counted_iterator operator-(int)
  requires bidirectional_iterator<I>;

Effects: Equivalent to: counted_iterator tmp = *this; --*this; return tmp;

constexpr counted_iterator operator+(iter_difference_t<I> n) const
  requires random_access_iterator<I>;

Effects: Equivalent to: return counted_iterator(current + n, length - n);

friend constexpr counted_iterator operator+(
  iter_difference_t<I> n, const counted_iterator& x)
    requires random_access_iterator<I>;

Effects: Equivalent to: return x + n;

constexpr counted_iterator& operator+=(iter_difference_t<I> n)
  requires random_access_iterator<I>;

Effects: Equivalent to: current += n; length -= n; return *this;

constexpr counted_iterator operator-(iter_difference_t<I> n) const
  requires random_access_iterator<I>;

Effects: Equivalent to: return counted_iterator(current - n, length + n);

template<common_with<I> I2>
  friend constexpr iter_difference_t<I2> operator-(
    const counted_iterator& x, const counted_iterator<I2>& y);

Preconditions: x and y refer to elements of the same sequence ([counted.iterator]).

Effects: Equivalent to: return y.length - x.length;

friend constexpr iter_difference_t<I> operator-(
  const counted_iterator& x, default_sentinel_t) noexcept;

Effects: Equivalent to: return -x.length;

friend constexpr iter_difference_t<I> operator-(
  default_sentinel_t, const counted_iterator& y) noexcept;

Effects: Equivalent to: return y.length;

constexpr counted_iterator& operator-=(iter_difference_t<I> n)
  requires random_access_iterator<I>;

Effects: Equivalent to: current -= n; length += n; return *this;

24 Iterators library [iterators]