boost::gil::scanline_read_iterator::operator*

constexpr
auto
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 */);