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Minor design documentation changes

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Mateusz Pusz
2019-09-30 11:08:52 +02:00
parent 0f803a1c2e
commit 7522b8a9fd
1 changed files with 8 additions and 7 deletions
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doc/DESIGN.md
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@@ -513,9 +513,10 @@ struct downcast_base {
`units::downcast_base` is a class that implements CRTP idiom, marks the base of downcasting `units::downcast_base` is a class that implements CRTP idiom, marks the base of downcasting
facility with a `base_type` member type, and provides a declaration of downcasting ADL friendly facility with a `base_type` member type, and provides a declaration of downcasting ADL friendly
(Hidden Friend) entry point member function `downcast_guide` that here does not return any specific (Hidden Friend) entry point member function `downcast_guide`. An important design point is that
type. This non-member function is going to be defined in a child class template `downcast_helper` this function does not return any specific type in its declaration. This non-member function
and will return a target type of the downcasting operation. is going to be defined in a child class template `downcast_helper` and will return a target
type of the downcasting operation there.
```cpp ```cpp
template<typename T> template<typename T>
@@ -538,7 +539,7 @@ struct downcast_helper : T {
`units::downcast_helper` is another CRTP class template that provides the implementation of a `units::downcast_helper` is another CRTP class template that provides the implementation of a
non-member friend function of the `downcast_base` class template which defines the target non-member friend function of the `downcast_base` class template which defines the target
type of downcasting operation. It is used in the following way to define `dimension` and type of a downcasting operation. It is used in the following way to define `dimension` and
`unit` types in the library: `unit` types in the library:
```cpp ```cpp
@@ -551,7 +552,7 @@ template<typename Child, Dimension D>
struct derived_unit<Child, D, R> : downcast_helper<Child, unit<D, ratio<1>>> {}; struct derived_unit<Child, D, R> : downcast_helper<Child, unit<D, ratio<1>>> {};
``` ```
With such CRTP types the only thing the user has to do to register a new type to a downcasting With such CRTP types the only thing the user has to do to register a new type to the downcasting
facility is to publicly derive from one of those CRTP types and provide its new child type as facility is to publicly derive from one of those CRTP types and provide its new child type as
the first template parameter of the CRTP type. the first template parameter of the CRTP type.
@@ -578,8 +579,8 @@ using common_rep = decltype(lhs.count() * rhs.count());
using ret = quantity<downcast_target<unit<dim, ratio_multiply<typename U1::ratio, typename U2::ratio>>>, common_rep>; using ret = quantity<downcast_target<unit<dim, ratio_multiply<typename U1::ratio, typename U2::ratio>>>, common_rep>;
``` ```
`detail::downcast_target_impl` checks if downcasting target is registered for the specific base class. `detail::downcast_target_impl` checks if a downcasting target is registered for the specific base class.
If yes, it returns the registered type. Otherwise, it works like a regular identity type returning If yes, it returns the registered type, otherwise it works like a regular identity type returning
a provided base class. a provided base class.
```cpp ```cpp