...

cxx/mcc_traits.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <chrono>
 #include <format>
 #include <ranges>
 
@@ -38,6 +39,15 @@ 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
+concept mcc_time_duration_c = requires {
+    []<class Rep, class Period>(std::type_identity<std::chrono::duration<Rep, Period>>) {
+
+    }(std::type_identity<std::remove_cvref_t<T>>());
+};
+
+
 /*  a callable concept and its signature traits   */
 
 template <typename T>