...

include/snipplib/containers/snplib_hmap.h

@@ -663,7 +663,9 @@ public:
             using u_t = std::invoke_result_t<decltype(from_cnv_func), v_t>::value_type;
 
             // user type must differ from inserted one
-            static_assert(!std::same_as<v_t, u_t>, "INVALID CONVERSIONAL 'FROM-FUNCTION' SIGNATURE!");
+            if constexpr (std::same_as<v_t, u_t>) {  // just ignore the such type
+                return;
+            }
 
             _getter<u_t>[this].emplace(
                 kk,