std::counted_iterator::operator++,+,+=,--,-,-=(3)

NAME
std::counted_iterator::operator++,+,+=,--,-,-= - std::counted_iterator::operator++,+,+=,--,-,-=

Synopsis
   constexpr counted_iterator& operator++(); (1) (since C++20)
   constexpr decltype(auto) operator++( int ); (2) (since C++20)
   constexpr counted_iterator operator++( int ) (3) (since C++20)
       requires std::forward_iterator<I>;
   constexpr counted_iterator& operator--() (4) (since C++20)
       requires std::bidirectional_iterator<I>;
   constexpr counted_iterator operator--( int ) (5) (since C++20)
       requires std::bidirectional_iterator<I>;
   constexpr counted_iterator operator+( std::iter_difference_t<I> n
   ) const (6) (since C++20)
       requires std::random_access_iterator<I>;
   constexpr counted_iterator& operator+=( std::iter_difference_t<I>
   n ) (7) (since C++20)
       requires std::random_access_iterator<I>;
   constexpr counted_iterator operator-( std::iter_difference_t<I> n
   ) const (8) (since C++20)
       requires std::random_access_iterator<I>;
   constexpr counted_iterator& operator-=( std::iter_difference_t<I>
   n ) (9) (since C++20)
       requires std::random_access_iterator<I>;
   Increments or decrements the underlying iterator current and the distance to the end
   length.
   The behavior of these functions is undefined if the length would be set to a minus
   value.
   1) Pre-increments by one. Equivalent to ++current; --length; return *this;.
   2) Post-increments by one. Equivalent to --length; try { return current++; }
   catch(...) { ++length; throw; }.
   3) Post-increments by one. Equivalent to counted_iterator temp{*this}; ++*this;
   return temp;.
   4) Pre-decrements by one. Equivalent to --current; ++length; return *this;.
   5) Post-decrements by one. Equivalent to counted_iterator temp{*this}; --*this;
   return temp;.
   6) Returns an iterator adaptor which is advanced by n. Equivalent to return
   counted_iterator(current + n, length - n);.
   7) Advances the iterator adaptor by n. Equivalent to current += n; length -= n;
   return *this;.
   8) Returns an iterator adaptor which is advanced by -n. Equivalent to return
   counted_iterator(current - n, length + n);.
   9) Advances the iterator adaptor by -n. Equivalent to current -= n; length += n;
   return *this;.

Parameters
   n - the number of positions to increment or decrement the iterator adaptor

Return value
   1) *this
   2,3) A copy of *this that was made before the change.
   4) *this
   5) A copy of *this that was made before the change.
   6) An iterator adaptor which is advanced by n.
   7) *this
   8) An iterator adaptor which is advanced by -n.
   9) *this

Example
// Run this code
 #include <cassert>
 #include <initializer_list>
 #include <iterator>
 int main()
 {
     const auto v = {1, 2, 3, 4, 5, 6};
     std::counted_iterator<std::initializer_list<int>::iterator> it1{v.begin(), 5};
     ++it1; assert(*it1 == 2 && it1.count() == 4); // (1)
     auto it2 = it1++; assert(*it2 == 2 && *it1 == 3); // (3)
     --it1; assert(*it1 == 2 && it1.count() == 4); // (4)
     auto it3 = it1--; assert(*it3 == 2 && *it1 == 1); // (5)
     auto it4 = it1 + 3; assert(*it4 == 4 && it4.count() == 2); // (6)
     auto it5 = it4 - 3; assert(*it5 == 1 && it5.count() == 5); // (8)
     it1 += 3; assert(*it1 == 4 && it1.count() == 2); // (7)
     it1 -= 3; assert(*it1 == 1 && it1.count() == 5); // (9)
 }

See also
   operator+ advances the iterator
   (C++20) (function template)
   operator- computes the distance between two iterator adaptors
   (C++20) (function template)