More constraints added for Dimension and Unit concepts

src/include/units/bits/stdconcepts.h

@@ -39,5 +39,10 @@ namespace mp {
         static_cast<To>(f());
       };
 
+    template<class Derived, class Base>
+    concept bool DerivedFrom =
+      std::is_base_of_v<Base, Derived> &&
+      std::is_convertible_v<const volatile Derived*, const volatile Base*>;
+
   }  // namespace std_concepts
 }  // namespace mp

src/include/units/dimension.h

@@ -101,7 +101,10 @@ namespace units {
   }  // namespace detail
 
   template<typename T>
-  concept bool Dimension = detail::is_dimension<typename T::type>;
+  concept bool Dimension =
+      std::is_empty_v<T> &&
+      detail::is_dimension<typename T::type> &&
+      DerivedFrom<T, typename T::type>;
 
 
   // dim_invert

src/include/units/unit.h

@@ -47,7 +47,10 @@ namespace units {
   }
 
   template<typename T>
-  concept bool Unit = detail::is_unit<typename T::type>;
+  concept bool Unit =
+      std::is_empty_v<T> &&
+      detail::is_unit<typename T::type> &&
+      DerivedFrom<T, typename T::type>;
 
   // dimension_traits