boost::gil::position_iterator::operator++

constexpr
position_iterator&
operator++() noexcept;

constexpr
position_iterator
operator++(int) noexcept;

constexpr
decltype(auto)
operator++(this auto& self)
requires requires { self += difference_type(1); };

constexpr
auto
operator++(this
    auto& self,
    int)
requires requires { ++self; };