boost::gil::position_iterator::operator*

constexpr
reference
operator*() const noexcept;

template<typename D = Derived>
constexpr
decltype(*access::base(std::declval<D const &>()))
operator*() const noexcept(/* see-below */);

template<typename D = Derived>
constexpr
decltype(*access::base(std::declval<D &>()))
operator*() noexcept(/* see-below */);