feat: ReferenceOf concept added

src/core/include/mp_units/bits/quantity_concepts.h

@@ -48,15 +48,13 @@ template<typename T>
 concept Quantity = requires(T* t) { detail::to_base_specialization_of_quantity(t); };
 
 /**
- * @brief A concept matching all quantities with provided dimension or reference
+ * @brief A concept matching all quantities with provided dimension or quantity spec
  *
- * Satisfied by all quantities with a dimension/reference being the instantiation derived from
- * the provided dimension/reference type.
+ * Satisfied by all quantities with a dimension/quantity_spec being the instantiation derived from
+ * the provided dimension/quantity_spec type.
  */
 template<typename Q, auto V>
-concept QuantityOf =
-  Quantity<Q> && ((Dimension<std::remove_const_t<decltype(V)>> && Q::dimension == V) ||
-                  (QuantitySpec<std::remove_const_t<decltype(V)>> && implicitly_convertible(Q::quantity_spec, V)));
+concept QuantityOf = Quantity<Q> && ReferenceOf<std::remove_const_t<decltype(Q::reference)>, V>;
 
 /**
  * @brief A concept matching all external quantities like types

src/core/include/mp_units/bits/quantity_point_concepts.h

@@ -68,7 +68,8 @@ concept PointOrigin = QuantityPoint<T> || detail::is_derived_from_specialization
  * Satisfied by all quantity point origins that are defined using a provided quantity specification.
  */
 template<typename T, auto Q>
-concept PointOriginFor = PointOrigin<T> && QuantitySpec<std::remove_const_t<decltype(Q)>> && implicitly_convertible(Q, T::quantity_spec);
+concept PointOriginFor =
+  PointOrigin<T> && QuantitySpec<std::remove_const_t<decltype(Q)>> && implicitly_convertible(Q, T::quantity_spec);
 
 template<Reference auto R, PointOriginFor<get_quantity_spec(R)> auto PO,
          RepresentationOf<get_quantity_spec(R).character> Rep>
@@ -86,16 +87,16 @@ inline constexpr bool is_quantity_point<T> = true;
 }  // namespace detail
 
 /**
- * @brief A concept matching all quantity points with provided dimension or reference
+ * @brief A concept matching all quantity points with provided dimension or quantity spec
  *
- * Satisfied by all quantity points with a dimension/reference being the instantiation derived from
- * the provided dimension/reference type.
+ * Satisfied by all quantity points with a dimension/quantity_spec being the instantiation derived from
+ * the provided dimension/quantity_spec type, or quantity points having the origin with the same
+ * `absolute_point_origin`.
  */
 template<typename QP, auto V>
 concept QuantityPointOf =
   QuantityPoint<QP> &&
-  ((Dimension<std::remove_const_t<decltype(V)>> && QP::dimension == V) ||
-   (QuantitySpec<std::remove_const_t<decltype(V)>> && implicitly_convertible(QP::quantity_spec, V)) ||
+  (ReferenceOf<std::remove_const_t<decltype(QP::reference)>, V> ||
    (PointOrigin<std::remove_const_t<decltype(V)>> &&
     std::same_as<std::remove_const_t<decltype(QP::absolute_point_origin)>, std::remove_const_t<decltype(V)>>));
 

src/core/include/mp_units/bits/reference_concepts.h

@@ -48,4 +48,32 @@ inline constexpr bool is_specialization_of_reference<reference<Q, U>> = true;
 template<typename T>
 concept Reference = AssociatedUnit<T> || detail::is_specialization_of_reference<T>;
 
+[[nodiscard]] consteval QuantitySpec auto get_quantity_spec(AssociatedUnit auto u);
+
+template<auto Q, auto U>
+[[nodiscard]] consteval QuantitySpec auto get_quantity_spec(reference<Q, U>)
+{
+  return Q;
+}
+
+[[nodiscard]] consteval Unit auto get_unit(AssociatedUnit auto u) { return u; }
+
+template<auto Q, auto U>
+[[nodiscard]] consteval Unit auto get_unit(reference<Q, U>)
+{
+  return U;
+}
+
+/**
+ * @brief A concept matching all references with provided dimension or quantity spec
+ *
+ * Satisfied by all references with a dimension/quantity_spec being the instantiation derived from
+ * the provided dimension/quantity_spec type.
+ */
+template<typename T, auto V>
+concept ReferenceOf =
+  Reference<T> &&
+  ((Dimension<std::remove_const_t<decltype(V)>> && get_quantity_spec(T{}).dimension == V) ||
+   (QuantitySpec<std::remove_const_t<decltype(V)>> && implicitly_convertible(get_quantity_spec(T{}), V)));
+
 }  // namespace mp_units

src/core/include/mp_units/reference.h

@@ -34,20 +34,6 @@ namespace mp_units {
   return detail::get_associated_quantity(u);
 }
 
-template<auto Q, auto U>
-[[nodiscard]] consteval QuantitySpec auto get_quantity_spec(reference<Q, U>)
-{
-  return Q;
-}
-
-[[nodiscard]] consteval Unit auto get_unit(AssociatedUnit auto u) { return u; }
-
-template<auto Q, auto U>
-[[nodiscard]] consteval Unit auto get_unit(reference<Q, U>)
-{
-  return U;
-}
-
 /**
  * @brief Quantity reference type
  *