萃取awaitor的特征

librf/src/type_traits.inl

@@ -104,5 +104,17 @@ RESUMEF_NS
 		{
 			return detail::get_awaitor_impl(static_cast<T&&>(value), 123);
 		}
-}
+
+		template<class _Ty, class = std::void_t<>>
+		struct awaitor_traits{};
+
+		template<class _Ty>
+		struct awaitor_traits<_Ty, 
+			std::void_t<decltype(get_awaitor(std::declval<_Ty>()))>
+		>
+		{
+			using type = decltype(get_awaitor(std::declval<_Ty>()));
+			using value_type = decltype(std::declval<type>().await_resume());
+		};
+	}
 }

librf/src/when_v2.h

@@ -97,17 +97,9 @@ RESUMEF_NS
 			using value_type = ignore_type;
 		};
 
-		template<class _Ty>
-		struct get_await_resume_result_type
-		{
-			using value_type = decltype(std::declval<std::remove_reference_t<_Ty>>().await_resume());
-		};
-
 		template<class _Ty>
 		using awaitor_result_t = typename convert_void_2_ignore<
-				typename get_await_resume_result_type<
-					decltype(traits::get_awaitor(std::declval<_Ty>()))
-				>::value_type
+			typename traits::awaitor_traits<_Ty>::value_type
 		>::value_type;