refactor: 💥 from now on point origins must be marked final + absolute_point_origin does not use CRTP anymore

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);