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; };