Function optional_map_impl

include/sol/optional_implementation.hpp:1641–1643

		template <class Opt, class F, class Ret = decltype(detail::invoke(std::declval<F>(), *std::declval<Opt>())),
		     detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
		constexpr auto optional_map_impl(Opt&& opt, F&& f) {
			return opt.has_value() ? detail::invoke(std::forward<F>(f), *std::forward<Opt>(opt)) : optional<Ret>(nullopt);
		}

		template <class Opt, class F, class Ret = decltype(detail::invoke(std::declval<F>(), *std::declval<Opt>())),
		     detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>