refactor: small detail namespace cleanup for units

Author: mpusz

src/core/include/mp-units/framework/unit.h

@@ -120,25 +120,23 @@ struct get_canonical_unit_result {
   inline static constexpr auto value = get_canonical_unit_impl(U{}, U{});
 };
 
-template<Unit Lhs, Unit Rhs>
-struct unit_less : std::bool_constant<type_name<Lhs>() < type_name<Rhs>()> {};
+}  // namespace detail
 
-template<typename T1, typename T2>
-using type_list_of_unit_less = expr_less<T1, T2, unit_less>;
+// TODO this should really be in the `details` namespace but is used in `chrono.h` (a part of mp_units.systems)
+// Even though it is not exported, it is visible to the other module via ADL
+[[nodiscard]] consteval auto get_canonical_unit(Unit auto u)
+{
+  return detail::get_canonical_unit_result<decltype(u)>::value;
+}
+
+namespace detail {
 
 template<typename From, typename To>
 concept PotentiallyConvertibleTo = Unit<From> && Unit<To> &&
                                    ((AssociatedUnit<From> && AssociatedUnit<To> &&
                                      implicitly_convertible(get_quantity_spec(From{}), get_quantity_spec(To{}))) ||
                                     (!AssociatedUnit<From> && !AssociatedUnit<To>));
 
-}  // namespace detail
-
-// TODO this should really be in the `details` namespace but is used in `chrono.h` (a part of mp_units.systems)
-// Even though it is not exported, it is visible to the other module via ADL
-[[nodiscard]] consteval auto get_canonical_unit(Unit auto u)
-{
-  return detail::get_canonical_unit_result<decltype(u)>::value;
 }
 
 // convertible
@@ -159,6 +157,12 @@ struct derived_unit;
 
 namespace detail {
 
+template<Unit Lhs, Unit Rhs>
+struct unit_less : std::bool_constant<type_name<Lhs>() < type_name<Rhs>()> {};
+
+template<typename T1, typename T2>
+using type_list_of_unit_less = expr_less<T1, T2, unit_less>;
+
 struct unit_interface {
   /**
    * Multiplication by `1` returns the same unit, otherwise `scaled_unit` is being returned.