fix: LA support fixed

src/CMakeLists.txt

@@ -28,6 +28,9 @@ set(projectPrefix UNITS_)
 option(${projectPrefix}AS_SYSTEM_HEADERS "Exports library as system headers" OFF)
 message(STATUS "${projectPrefix}AS_SYSTEM_HEADERS: ${${projectPrefix}AS_SYSTEM_HEADERS}")
 
+option(${projectPrefix}BUILD_LA "Build code depending on the linear algebra library" ON)
+message(STATUS "${projectPrefix}BUILD_LA: ${${projectPrefix}BUILD_LA}")
+
 list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
 
 include(AddUnitsModule)

src/core/include/units/bits/basic_concepts.h

@@ -401,8 +401,11 @@ concept castable_number_ =  // exposition only
 
 template<typename T>
 concept scalable_ =  // exposition only
-  castable_number_<T> || (requires { typename T::value_type; } && castable_number_<typename T::value_type> &&
-                          scalable_number_<T, std::common_type_t<typename T::value_type, std::intmax_t>>);
+  castable_number_<T> ||
+  (requires { typename T::value_type; } && castable_number_<typename T::value_type> &&
+   scalable_number_<T, std::common_type_t<typename T::value_type, std::intmax_t>>) ||
+  (requires { typename T::element_type; } && castable_number_<typename T::element_type> &&
+   scalable_number_<T, std::common_type_t<typename T::element_type, std::intmax_t>>);
 
 template<typename T, typename U>
 concept scalable_with_ =  // exposition only
@@ -420,6 +423,12 @@ inline constexpr bool is_wrapped_quantity<T> =
   Quantity<typename T::value_type> || QuantityLike<typename T::value_type> ||
   is_wrapped_quantity<typename T::value_type>;
 
+template<typename T>
+  requires requires { typename T::element_type; }
+inline constexpr bool is_wrapped_quantity<T> =
+  Quantity<typename T::element_type> || QuantityLike<typename T::element_type> ||
+  is_wrapped_quantity<typename T::element_type>;
+
 template<typename T>
   requires requires { typename T::quantity_type; }
 inline constexpr bool is_wrapped_quantity<T> = Quantity<typename T::quantity_type>;
@@ -429,8 +438,9 @@ inline constexpr bool is_wrapped_quantity<T> = Quantity<typename T::quantity_typ
 /**
  * @brief A concept matching types that wrap quantity objects.
  *
- * Satisfied by all wrapper types that satisfy `Quantity<typename T::value_type>`
- * recursively (i.e. `std::optional<si::length<si::metre>>`).
+ * Satisfied by all wrapper types that satisfy `Quantity<typename T::value_type>` or
+ * `Quantity<typename T::element_type>` recursively
+ * (i.e. `std::optional<si::length<si::metre>>`).
  */
 template<typename T>
 concept wrapped_quantity_ =  // exposition only

src/core/include/units/customization_points.h

@@ -44,6 +44,10 @@ template<typename T>
   requires requires { typename T::value_type; }
 inline constexpr bool treat_as_floating_point<T> = treat_as_floating_point<typename T::value_type>;
 
+template<typename T>
+  requires requires { typename T::element_type; }
+inline constexpr bool treat_as_floating_point<T> = treat_as_floating_point<typename T::element_type>;
+
 /**
  * @brief A type trait that defines zero, one, min, and max for a representation type
  *

src/core/include/units/quantity_cast.h

@@ -83,6 +83,16 @@ struct cast_traits<From, To> {
   using rep_type = std::common_type_t<From, To>;
 };
 
+template<typename From, typename To>
+  requires(!common_type_with_<std::common_type_t<From, To>, std::intmax_t> &&
+           scalable_number_<std::common_type_t<From, To>, std::intmax_t> &&
+           requires { typename std::common_type_t<From, To>::element_type; } &&
+           common_type_with_<typename std::common_type_t<From, To>::element_type, std::intmax_t>)
+struct cast_traits<From, To> {
+  using ratio_type = std::common_type_t<typename std::common_type_t<From, To>::element_type, std::intmax_t>;
+  using rep_type = std::common_type_t<From, To>;
+};
+
 }  // namespace detail
 
 /**