...

cxx/mcc_traits.h

@@ -39,8 +39,8 @@ concept mcc_formattable =
     requires(T v, std::format_context ctx) { std::formatter<std::remove_cvref_t<T>>().format(v, ctx); };
 
 
-template <typename T>
 // from https://stackoverflow.com/questions/74383254/concept-that-models-only-the-stdchrono-duration-types
+template <typename T>
 concept mcc_time_duration_c = requires {
     []<class Rep, class Period>(std::type_identity<std::chrono::duration<Rep, Period>>) {
 
@@ -48,6 +48,12 @@ concept mcc_time_duration_c = requires {
 };
 
 
+template <typename T>
+concept mcc_systime_c = requires {
+    []<class DT>(std::type_identity<std::chrono::sys_time<DT>>) {}(std::type_identity<std::remove_cvref_t<T>>());
+};
+
+
 /*  a callable concept and its signature traits   */
 
 template <typename T>