is_nothrow_convertible_cpp17.hpp

// std::is_nothrow_convertible(added since C++2a) implementation in C++17.
namespace std{
	namespace _details{
		template<typename To>
		std::void_t<To()> convert_to(To) noexcept;
		
		template<typename From, typename To, typename = void>
		struct is_nothrow_convertible_imp : std::false_type{};

		template<typename From, typename To>
		struct is_nothrow_convertible_imp<From, To, typename std::enable_if<noexcept(std::_details::convert_to<To>(std::declval<From>()))>::type> : std::true_type{};
	}

	template<typename From, typename To>
	struct is_nothrow_convertible : std::conditional<
		std::is_void<From>::value,
		std::is_void<To>,
		_details::is_nothrow_convertible_imp<From, To>
	>::type{};
}