refactor: 💥 from now on point origins must be marked final + `absol…

…ute_point_origin` does not use CRTP anymore

CHANGELOG.md

@@ -10,7 +10,7 @@
 - (!) feat: ABI concerns resolved with introduction of u8 strings for symbols
 - (!) feat: API-related Conan, CMake, and preprocessor options redesigned
 - (!) feat: `core.h` removed
-- (!) feat: from now on units, dimensions, and quantity specifications have to be marked as `final`
+- (!) feat: from now on units, dimensions, quantity specifications, and point origins have to be marked as `final`
 - feat: implicit point origins support added
 - feat: unit default point origin support added
 - feat: `fma`, `isfinite`, `isinf`, and `isnan` math function added by [@NAThompson](https://github.com/NAThompson)
@@ -47,6 +47,7 @@
 - (!) refactor: `framework.h` introduced
 - (!) refactor: type list tools made an implementation detail of the library
 - (!) refactor: header files with the entire system definitions moved up in the directory tree
+- (!) refactor: `absolute_point_origin` does not use CRTP anymore
 - refactor: system's units do not inherit from one another anymore
 - refactor: all units made `final`
 - refactor: math functions constraints refactored

docs/blog/posts/2.2.0-released.md

@@ -205,7 +205,7 @@ origins. For example:
 === "Before"
 
     ```cpp
-    constexpr struct zero : absolute_point_origin<zero, currency> {} zero;
+    constexpr struct zero final : absolute_point_origin<currency> {} zero;
 
     quantity_point price_usd = zero + 100 * USD;
     ```
@@ -300,25 +300,43 @@ is why it was renamed to `symbol_text` (:boom: **breaking change** :boom:).
     ```
 
 
-## Changes to dimension and quantity specification definitions
+## Changes to dimension, quantity specification, and point origins definitions
 
-Similarly to units, now also all dimensions and quantity specifications have to be marked final
-(:boom: **breaking change** :boom:).
+Similarly to units, now also all dimensions, quantity specifications, and point origins have to be
+marked `final` (:boom: **breaking change** :boom:).
 
 === "Now"
 
     ```cpp
     inline constexpr struct dim_length final : base_dimension<"L"> {} dim_length;
     inline constexpr struct length final : quantity_spec<dim_length> {} length;
+
+    inline constexpr struct absolute_zero final : absolute_point_origin<isq::thermodynamic_temperature> {} absolute_zero;
+    inline constexpr auto zeroth_kelvin  = absolute_zero;
+    inline constexpr struct kelvin final : named_unit<"K", kind_of<isq::thermodynamic_temperature>, zeroth_kelvin> {} kelvin;
+
+    inline constexpr struct ice_point final : relative_point_origin<quantity_point{273'150 * milli<kelvin>}> {} ice_point;
+    inline constexpr auto zeroth_degree_Celsius = ice_point;
+    inline constexpr struct degree_Celsius final : named_unit<symbol_text{u8"°C", "`C"}, kelvin, zeroth_degree_Celsius> {} degree_Celsius;
     ```
 
 === "Before"
 
     ```cpp
     inline constexpr struct dim_length : base_dimension<"L"> {} dim_length;
     inline constexpr struct length : quantity_spec<dim_length> {} length;
+
+    inline constexpr struct absolute_zero : absolute_point_origin<absolute_zero, isq::thermodynamic_temperature> {} absolute_zero;
+    inline constexpr struct zeroth_kelvin : decltype(absolute_zero) {} zeroth_kelvin;
+    inline constexpr struct kelvin : named_unit<"K", kind_of<isq::thermodynamic_temperature>, zeroth_kelvin> {} kelvin;
+
+    inline constexpr struct ice_point : relative_point_origin<quantity_point{273'150 * milli<kelvin>}> {} ice_point;
+    inline constexpr struct zeroth_degree_Celsius : decltype(ice_point) {} zeroth_degree_Celsius;
+    inline constexpr struct degree_Celsius : named_unit<symbol_text{u8"°C", "`C"}, kelvin, zeroth_degree_Celsius> {} degree_Celsius;
     ```
 
+Please also note, that the `absolute_point_origin` does not use CRTP idiom anymore (:boom: **breaking change** :boom:).
+
 
 ## Improved text output
 

docs/users_guide/framework_basics/concepts.md

@@ -16,6 +16,8 @@ or derived [quantity](../../appendix/glossary.md#quantity):
   by the library's framework based on the [quantity equation](../../appendix/glossary.md#quantity-equation)
   provided in the [quantity specification](../../appendix/glossary.md#quantity_spec).
 
+All of the above dimensions have to be marked as `final`.
+
 
 ### `DimensionOf<T, V>` { #DimensionOf }
 
@@ -42,6 +44,8 @@ including:
 - Intermediate [derived quantity](../../appendix/glossary.md#derived-quantity) specifications being
   a result of a [quantity equations](../../appendix/glossary.md#quantity-equation) on other specifications.
 
+All of the above quantity specifications have to be marked as `final`.
+
 
 ### `QuantitySpecOf<T, V>` { #QuantitySpecOf }
 
@@ -237,7 +241,7 @@ implicitly convertible from quantity specification `V`, which means that `V` mus
     However, if we define `mean_sea_level` in the following way:
 
     ```cpp
-    inline constexpr struct mean_sea_level : absolute_point_origin<isq::altitude> {} mean_sea_level;
+    inline constexpr struct mean_sea_level final : absolute_point_origin<isq::altitude> {} mean_sea_level;
     ```
 
     then it can't be used as a point origin for _points_ of `isq::length` or `isq::width` as none of them
@@ -330,7 +334,7 @@ for which an instantiation of `quantity_point_like_traits` type trait yields a v
     struct mp_units::quantity_point_like_traits<std::chrono::time_point<C, std::chrono::seconds>> {
       using T = std::chrono::time_point<C, std::chrono::seconds>;
       static constexpr auto reference = si::second;
-      static constexpr struct point_origin : absolute_point_origin<isq::time> {} point_origin{};
+      static constexpr struct point_origin final : absolute_point_origin<isq::time> {} point_origin{};
       using rep = std::chrono::seconds::rep;
 
       [[nodiscard]] static constexpr convert_implicitly<quantity<reference, rep>> to_quantity(const T& qp)

docs/users_guide/framework_basics/design_overview.md

@@ -346,13 +346,13 @@ For example:
 - the absolute point origin can be defined in the following way:
 
   ```cpp
-  inline constexpr struct absolute_zero : absolute_point_origin<isq::thermodynamic_temperature> {} absolute_zero;
+  inline constexpr struct absolute_zero final : absolute_point_origin<isq::thermodynamic_temperature> {} absolute_zero;
   ```
 
 - the relative point origin can be defined in the following way:
 
   ```cpp
-  inline constexpr struct ice_point : relative_point_origin<absolute_zero + 273'150 * milli<kelvin>> {} ice_point;
+  inline constexpr struct ice_point final : relative_point_origin<absolute_zero + 273'150 * milli<kelvin>> {} ice_point;
   ```
 
 

docs/users_guide/framework_basics/the_affine_space.md

@@ -172,7 +172,7 @@ origin.
 ![affine_space_2](affine_space_2.svg){style="width:80%;display: block;margin: 0 auto;"}
 
 ```cpp
-inline constexpr struct origin : absolute_point_origin<origin, isq::distance> {} origin;
+inline constexpr struct origin final : absolute_point_origin<isq::distance> {} origin;
 
 // quantity_point<si::metre, origin> qp1{100 * m};  // Compile-time error
 // quantity_point<si::metre, origin> qp2{120 * m};  // Compile-time error
@@ -197,14 +197,6 @@ assert(origin - qp2 == -120 * m);
 // assert(origin - origin == 0 * m);   // Compile-time error
 ```
 
-!!! info
-
-    The `absolute_point_origin` class template uses the CRTP idiom to enforce the uniqueness of
-    such a type. You should pass the type of a derived class as the first argument of the template
-    instantiation.
-
-*[CRTP]: Curiously Recurring Template Parameter
-
 We can't construct a quantity point directly from the quantity anymore when a custom, named origin
 is used. To prevent potential safety and maintenance issues, we always need to
 explicitly provide both a compatible origin and a quantity measured from it to construct a quantity
@@ -249,8 +241,8 @@ type and unit is being used:
 ![affine_space_3](affine_space_3.svg){style="width:80%;display: block;margin: 0 auto;"}
 
 ```cpp
-inline constexpr struct origin1 : absolute_point_origin<origin1, isq::distance> {} origin1;
-inline constexpr struct origin2 : absolute_point_origin<origin2, isq::distance> {} origin2;
+inline constexpr struct origin1 final : absolute_point_origin<isq::distance> {} origin1;
+inline constexpr struct origin2 final : absolute_point_origin<isq::distance> {} origin2;
 
 quantity_point qp1 = origin1 + 100 * m;
 quantity_point qp2 = origin2 + 120 * m;
@@ -284,10 +276,10 @@ For such cases, relative point origins should be used:
 ![affine_space_4](affine_space_4.svg){style="width:80%;display: block;margin: 0 auto;"}
 
 ```cpp
-inline constexpr struct A : absolute_point_origin<A, isq::distance> {} A;
-inline constexpr struct B : relative_point_origin<A + 10 * m> {} B;
-inline constexpr struct C : relative_point_origin<B + 10 * m> {} C;
-inline constexpr struct D : relative_point_origin<A + 30 * m> {} D;
+inline constexpr struct A final : absolute_point_origin<isq::distance> {} A;
+inline constexpr struct B final : relative_point_origin<A + 10 * m> {} B;
+inline constexpr struct C final : relative_point_origin<B + 10 * m> {} C;
+inline constexpr struct D final : relative_point_origin<A + 30 * m> {} D;
 
 quantity_point qp1 = C + 100 * m;
 quantity_point qp2 = D + 120 * m;
@@ -392,17 +384,17 @@ point origins for this purpose:
 ```cpp
 namespace si {
 
-inline constexpr struct absolute_zero : absolute_point_origin<absolute_zero, isq::thermodynamic_temperature> {} absolute_zero;
-inline constexpr struct zeroth_kelvin : decltype(absolute_zero) {} zeroth_kelvin;
+inline constexpr struct absolute_zero final : absolute_point_origin<isq::thermodynamic_temperature> {} absolute_zero;
+inline constexpr auto zeroth_kelvin = absolute_zero;
 
-inline constexpr struct ice_point : relative_point_origin<quantity_point{273'150 * milli<kelvin>}> {} ice_point;
-inline constexpr struct zeroth_degree_Celsius : decltype(ice_point) {} zeroth_degree_Celsius;
+inline constexpr struct ice_point final : relative_point_origin<quantity_point{273'150 * milli<kelvin>}> {} ice_point;
+inline constexpr auto zeroth_degree_Celsius = ice_point;
 
 }
 
 namespace usc {
 
-inline constexpr struct zeroth_degree_Fahrenheit :
+inline constexpr struct zeroth_degree_Fahrenheit final :
   relative_point_origin<quantity_point{-32 * (mag_ratio<5, 9> * si::degree_Celsius)}> {} zeroth_degree_Fahrenheit;
 
 }
@@ -481,7 +473,7 @@ the following way:
 ![affine_space_6](affine_space_6.svg){style="width:80%;display: block;margin: 0 auto;"}
 
 ```cpp
-constexpr struct room_reference_temp : relative_point_origin<quantity_point{21 * deg_C}> {} room_reference_temp;
+constexpr struct room_reference_temp final : relative_point_origin<quantity_point{21 * deg_C}> {} room_reference_temp;
 using room_temp = quantity_point<isq::Celsius_temperature[deg_C], room_reference_temp>;
 
 constexpr auto step_delta = isq::Celsius_temperature(0.5 * deg_C);

docs/users_guide/use_cases/interoperability_with_other_libraries.md

@@ -256,8 +256,8 @@ include the _mp-units/systems/si/chrono.h_ file to benefit from it. This file pr
     to the `std::chrono` abstractions:
 
     ```cpp
-    inline constexpr struct ts_origin : relative_point_origin<chrono_point_origin<system_clock> + 1 * h> {} ts_origin;
-    inline constexpr struct my_origin : absolute_point_origin<my_origin, isq::time> {} my_origin;
+    inline constexpr struct ts_origin final : relative_point_origin<chrono_point_origin<system_clock> + 1 * h> {} ts_origin;
+    inline constexpr struct my_origin final : absolute_point_origin<isq::time> {} my_origin;
 
     quantity_point qp1 = sys_seconds{1s};
     auto tp1 = to_chrono_time_point(qp1);  // OK

example/include/geographic.h

@@ -40,7 +40,7 @@ import mp_units;
 
 namespace geographic {
 
-inline constexpr struct mean_sea_level : mp_units::absolute_point_origin<mean_sea_level, mp_units::isq::altitude> {
+inline constexpr struct mean_sea_level final : mp_units::absolute_point_origin<mp_units::isq::altitude> {
 } mean_sea_level;
 
 using msl_altitude = mp_units::quantity_point<mp_units::isq::altitude[mp_units::si::metre], mean_sea_level>;
@@ -68,10 +68,9 @@ struct MP_UNITS_STD_FMT::formatter<geographic::msl_altitude, Char> :
 
 namespace geographic {
 
-inline constexpr struct equator : mp_units::absolute_point_origin<equator, mp_units::isq::angular_measure> {
+inline constexpr struct equator final : mp_units::absolute_point_origin<mp_units::isq::angular_measure> {
 } equator;
-inline constexpr struct prime_meridian :
-    mp_units::absolute_point_origin<prime_meridian, mp_units::isq::angular_measure> {
+inline constexpr struct prime_meridian final : mp_units::absolute_point_origin<mp_units::isq::angular_measure> {
 } prime_meridian;
 
 

example/unmanned_aerial_vehicle.cpp

@@ -45,7 +45,7 @@ using namespace geographic;
 enum class earth_gravity_model : std::int8_t { egm84_15, egm95_5, egm2008_1 };
 
 template<earth_gravity_model M>
-struct height_above_ellipsoid_t : absolute_point_origin<height_above_ellipsoid_t<M>, isq::altitude> {
+struct height_above_ellipsoid_t final : absolute_point_origin<isq::altitude> {
   static constexpr earth_gravity_model egm = M;
 };
 template<earth_gravity_model M>
@@ -115,7 +115,7 @@ hae_altitude<M> to_hae(msl_altitude msl, position<long double> pos)
 // **** HAL ****
 
 // clang-format off
-inline constexpr struct height_above_launch : absolute_point_origin<height_above_launch, isq::altitude> {} height_above_launch;
+inline constexpr struct height_above_launch final : absolute_point_origin<isq::altitude> {} height_above_launch;
 // clang-format on
 
 using hal_altitude = quantity_point<isq::altitude[si::metre], height_above_launch>;

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

@@ -35,11 +35,10 @@
 
 namespace mp_units {
 
-MP_UNITS_EXPORT template<typename Derived, QuantitySpec auto QS>
+MP_UNITS_EXPORT template<QuantitySpec auto QS>
 // NOLINTNEXTLINE(bugprone-crtp-constructor-accessibility)
 struct absolute_point_origin {
   static constexpr QuantitySpec auto quantity_spec = QS;
-  using _type_ = absolute_point_origin;
 };
 
 MP_UNITS_EXPORT template<QuantityPoint auto QP>
@@ -56,7 +55,7 @@ struct relative_point_origin {
 };
 
 template<QuantitySpec auto QS>
-struct zeroth_point_origin_ : absolute_point_origin<zeroth_point_origin_<QS>, QS> {};
+struct zeroth_point_origin_ final : absolute_point_origin<QS> {};
 
 MP_UNITS_EXPORT template<QuantitySpec auto QS>
 inline constexpr zeroth_point_origin_<QS> zeroth_point_origin;
@@ -81,9 +80,8 @@ MP_UNITS_EXPORT template<PointOrigin PO1, PointOrigin PO2>
 [[nodiscard]] consteval bool operator==(PO1 po1, PO2 po2)
 {
   if constexpr (detail::AbsolutePointOrigin<PO1> && detail::AbsolutePointOrigin<PO2>)
-    return is_same_v<typename PO1::_type_, typename PO2::_type_> ||
-           (detail::is_zeroth_point_origin(po1) && detail::is_zeroth_point_origin(po2) &&
-            interconvertible(po1.quantity_spec, po2.quantity_spec));
+    return is_same_v<PO1, PO2> || (detail::is_zeroth_point_origin(po1) && detail::is_zeroth_point_origin(po2) &&
+                                   interconvertible(po1.quantity_spec, po2.quantity_spec));
   else if constexpr (detail::RelativePointOrigin<PO1> && detail::RelativePointOrigin<PO2>)
     return PO1::quantity_point == PO2::quantity_point;
   else if constexpr (detail::RelativePointOrigin<PO1>)

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

@@ -32,30 +32,23 @@
 
 namespace mp_units {
 
-MP_UNITS_EXPORT template<typename Derived, QuantitySpec auto QS>
+MP_UNITS_EXPORT template<QuantitySpec auto QS>
 struct absolute_point_origin;
 
 namespace detail {
 
 template<typename T>
 inline constexpr bool is_quantity_point = false;
 
-template<typename T>
-inline constexpr bool is_specialization_of_absolute_point_origin = false;
-
-template<typename D, auto Q>
-inline constexpr bool is_specialization_of_absolute_point_origin<absolute_point_origin<D, Q>> = true;
-
-template<typename D, auto Q>
-void to_base_specialization_of_absolute_point_origin(const volatile absolute_point_origin<D, Q>*);
+template<auto Q>
+void to_base_specialization_of_absolute_point_origin(const volatile absolute_point_origin<Q>*);
 
 template<typename T>
 inline constexpr bool is_derived_from_specialization_of_absolute_point_origin =
   requires(T* t) { to_base_specialization_of_absolute_point_origin(t); };
 
 template<typename T>
-concept AbsolutePointOrigin =
-  is_derived_from_specialization_of_absolute_point_origin<T> && !is_specialization_of_absolute_point_origin<T>;
+concept AbsolutePointOrigin = is_derived_from_specialization_of_absolute_point_origin<T> && std::is_final_v<T>;
 
 }  // namespace detail
 
@@ -72,12 +65,6 @@ struct relative_point_origin;
 
 namespace detail {
 
-template<typename T>
-inline constexpr bool is_specialization_of_relative_point_origin = false;
-
-template<auto QP>
-inline constexpr bool is_specialization_of_relative_point_origin<relative_point_origin<QP>> = true;
-
 template<auto QP>
 void to_base_specialization_of_relative_point_origin(const volatile relative_point_origin<QP>*);
 
@@ -86,8 +73,7 @@ inline constexpr bool is_derived_from_specialization_of_relative_point_origin =
   requires(T* t) { to_base_specialization_of_relative_point_origin(t); };
 
 template<typename T>
-concept RelativePointOrigin =
-  is_derived_from_specialization_of_relative_point_origin<T> && !is_specialization_of_relative_point_origin<T>;
+concept RelativePointOrigin = is_derived_from_specialization_of_relative_point_origin<T> && std::is_final_v<T>;
 
 }  // namespace detail
 

src/systems/include/mp-units/systems/si/chrono.h

@@ -85,7 +85,7 @@ struct quantity_like_traits<std::chrono::duration<Rep, Period>> {
 };
 
 template<typename C>
-struct chrono_point_origin_ : absolute_point_origin<chrono_point_origin_<C>, isq::time> {
+struct chrono_point_origin_ final : absolute_point_origin<isq::time> {
   using clock = C;
 };
 MP_UNITS_EXPORT template<typename C>

src/systems/include/mp-units/systems/si/units.h

@@ -44,8 +44,8 @@ inline constexpr struct gram final : named_unit<"g", kind_of<isq::mass>> {} gram
 inline constexpr auto kilogram = kilo<gram>;
 inline constexpr struct ampere final : named_unit<"A", kind_of<isq::electric_current>> {} ampere;
 
-inline constexpr struct absolute_zero : absolute_point_origin<absolute_zero, isq::thermodynamic_temperature> {} absolute_zero;
-inline constexpr struct zeroth_kelvin : decltype(absolute_zero) {} zeroth_kelvin;
+inline constexpr struct absolute_zero final : absolute_point_origin<isq::thermodynamic_temperature> {} absolute_zero;
+inline constexpr auto zeroth_kelvin  = absolute_zero;
 inline constexpr struct kelvin final : named_unit<"K", kind_of<isq::thermodynamic_temperature>, zeroth_kelvin> {} kelvin;
 
 inline constexpr struct mole final : named_unit<"mol", kind_of<isq::amount_of_substance>> {} mole;
@@ -77,8 +77,8 @@ inline constexpr struct weber final : named_unit<"Wb", volt * second> {} weber;
 inline constexpr struct tesla final : named_unit<"T", weber / square(metre)> {} tesla;
 inline constexpr struct henry final : named_unit<"H", weber / ampere> {} henry;
 
-inline constexpr struct ice_point : relative_point_origin<quantity_point{273'150 * milli<kelvin>}> {} ice_point;
-inline constexpr struct zeroth_degree_Celsius : decltype(ice_point) {} zeroth_degree_Celsius;
+inline constexpr struct ice_point final : relative_point_origin<quantity_point{273'150 * milli<kelvin>}> {} ice_point;
+inline constexpr auto zeroth_degree_Celsius = ice_point;
 inline constexpr struct degree_Celsius final : named_unit<symbol_text{u8"°C", "`C"}, kelvin, zeroth_degree_Celsius> {} degree_Celsius;
 
 inline constexpr struct lumen final : named_unit<"lm", candela * steradian> {} lumen;

src/systems/include/mp-units/systems/usc.h

@@ -118,7 +118,7 @@ inline constexpr struct troy_pound final : named_unit<"lb t", mag<12> * troy_onc
 inline constexpr struct inch_of_mercury final : named_unit<"inHg", mag_ratio<3'386'389, 1'000> * si::pascal> {} inch_of_mercury;
 
 // https://en.wikipedia.org/wiki/United_States_customary_units#Temperature
-inline constexpr struct zeroth_degree_Fahrenheit : relative_point_origin<quantity_point{-32 * (mag_ratio<5, 9> * si::degree_Celsius)}> {} zeroth_degree_Fahrenheit;
+inline constexpr struct zeroth_degree_Fahrenheit final : relative_point_origin<quantity_point{-32 * (mag_ratio<5, 9> * si::degree_Celsius)}> {} zeroth_degree_Fahrenheit;
 inline constexpr struct degree_Fahrenheit final : named_unit<symbol_text{u8"°F", "`F"}, mag_ratio<5, 9> * si::degree_Celsius, zeroth_degree_Fahrenheit> {} degree_Fahrenheit;
 
 // clang-format on