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README updated

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Mateusz Pusz
2019-04-11 13:54:51 +01:00
parent a49ef2d055
commit d572b50bee
1 changed files with 32 additions and 18 deletions
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doc/DESIGN.md
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@@ -39,7 +39,7 @@ static_assert(10_km / 5_km == 2);
3. No macros in the user interface
4. Easy extensibility
5. No external dependencies
6. Possibility to be standardized as a part of the C++ Standard Library
6. Possibility to be standardized as a freestanding part of the C++ Standard Library
## Basic Concepts
@@ -111,7 +111,7 @@ However, such an approach have some challenges:
constexpr Velocity auto v1 = 1_m / 1_s;
constexpr Velocity auto v2 = 2 / 2_s * 1_m;
static_assert(Same<decltype(v1), decltype(v2)>);
static_assert(std::Same<decltype(v1), decltype(v2)>);
static_assert(v1 == v2);
```
@@ -215,7 +215,7 @@ expressed in a specific unit of that dimension:
```cpp
template<Dimension D, Unit U, Number Rep>
requires Same<D, typename U::dimension>
requires std::Same<D, typename U::dimension>
class quantity;
```
@@ -233,7 +233,7 @@ member types and functions as below:
```cpp
template<Dimension D, Unit U, Number Rep>
requires Same<D, typename U::dimension>
requires std::Same<D, typename U::dimension>
class quantity {
public:
using dimension = D;
@@ -248,13 +248,13 @@ public:
template<Number Rep1, Dimension D, Unit U, Number Rep2>
quantity<dim_invert_t<D>, upcasting_traits_t<unit<dim_invert_t<D>, std::ratio<U::ratio::den, U::ratio::num>>>, std::common_type_t<Rep1, Rep2>>
constexpr operator/(const Rep1& v,
const quantity<D, U, Rep2>& q);
const quantity<D, U, Rep2>& q) [[expects: q != quantity<D, U, Rep2>(0)]];
template<Dimension D1, Unit U1, Number Rep1, Dimension D2, Unit U2, Number Rep2>
requires treat_as_floating_point<std::common_type_t<Rep1, Rep2>> || std::ratio_divide<typename U1::ratio, typename U2::ratio>::den == 1
quantity<dimension_divide_t<D1, D2>, upcasting_traits_t<unit<dimension_divide_t<D1, D2>, std::ratio_divide<typename U1::ratio, typename U2::ratio>>>, std::common_type_t<Rep1, Rep2>>
constexpr operator/(const quantity<D1, U1, Rep1>& lhs,
const quantity<D2, U2, Rep2>& rhs);
const quantity<D2, U2, Rep2>& rhs) [[expects: rhs != quantity<D, U2, Rep2>(0)]];
};
```
@@ -285,14 +285,14 @@ C:\repos\units\example\example.cpp:39:22: error: deduced initializer does not sa
^~~~
In file included from C:\repos\units\example\example.cpp:23:
C:/repos/units/src/include/units/si/velocity.h:41:16: note: within 'template<class T> concept const bool units::Velocity<T> [with T = units::quantity<units::dimension<units::exp<units::base_dim_time, 1> >, units::unit<units::dimension<units::exp<units::base_dim_time, 1> >, std::ratio<1> >, long long int>]'
concept Velocity = Quantity<T> && Same<typename T::dimension, dimension_velocity>;
concept Velocity = Quantity<T> && std::Same<typename T::dimension, dimension_velocity>;
^~~~~~~~
In file included from C:/repos/units/src/include/units/bits/tools.h:25,
from C:/repos/units/src/include/units/dimension.h:25,
from C:/repos/units/src/include/units/si/base_dimensions.h:25,
from C:/repos/units/src/include/units/si/velocity.h:25,
from C:\repos\units\example\example.cpp:23:
C:/repos/units/src/include/units/bits/stdconcepts.h:33:18: note: within 'template<class T, class U> concept const bool mp::std_concepts::Same<T, U> [with T = units::dimension<units::exp<units::base_dim_time, 1> >; U = units::dimension<units::exp<units::base_dim_length, 1>, units::exp<units::base_dim_time, -1> >]'
C:/repos/units/src/include/units/bits/stdconcepts.h:33:18: note: within 'template<class T, class U> concept const bool std::Same<T, U> [with T = units::dimension<units::exp<units::base_dim_time, 1> >; U = units::dimension<units::exp<units::base_dim_length, 1>, units::exp<units::base_dim_time, -1> >]'
concept Same = std::is_same_v<T, U>;
^~~~
C:/repos/units/src/include/units/bits/stdconcepts.h:33:18: note: 'std::is_same_v' evaluated to false
@@ -322,14 +322,14 @@ C:\repos\units\example\example.cpp:40:22: error: deduced initializer does not sa
^~~~
In file included from C:\repos\units\example\example.cpp:23:
C:/repos/units/src/include/units/si/velocity.h:48:16: note: within 'template<class T> concept const bool units::Velocity<T> [with T = units::quantity<units::dimension_time, units::second, long long int>]'
concept Velocity = Quantity<T> && Same<typename T::dimension, dimension_velocity>;
concept Velocity = Quantity<T> && std::Same<typename T::dimension, dimension_velocity>;
^~~~~~~~
In file included from C:/repos/units/src/include/units/bits/tools.h:25,
from C:/repos/units/src/include/units/dimension.h:25,
from C:/repos/units/src/include/units/si/base_dimensions.h:25,
from C:/repos/units/src/include/units/si/velocity.h:25,
from C:\repos\units\example\example.cpp:23:
C:/repos/units/src/include/units/bits/stdconcepts.h:33:18: note: within 'template<class T, class U> concept const bool mp::std_concepts::Same<T, U> [with T = units::dimension_time; U = units::dimension_velocity]'
C:/repos/units/src/include/units/bits/stdconcepts.h:33:18: note: within 'template<class T, class U> concept const bool std::Same<T, U> [with T = units::dimension_time; U = units::dimension_velocity]'
concept Same = std::is_same_v<T, U>;
^~~~
C:/repos/units/src/include/units/bits/stdconcepts.h:33:18: note: 'std::is_same_v' evaluated to false
@@ -379,36 +379,50 @@ template<> struct upcasting_traits<upcast_from<kilometer>> : upcast_to<kilometer
```
## Adding new dimensions
## Adding new derived dimensions
In order to extend the library with custom dimensions the user has to:
1. Create a new dimension type and provide upcasting trait for it:
1. Create a new dimension type with the recipe of how to construct it from base dimensions and provide
upcasting trait for it:
```cpp
struct dimension_velocity : make_dimension_t<exp<base_dim_length, 1>, exp<base_dim_time, -1>> {};
template<> struct upcasting_traits<upcast_from<dimension_velocity>> : upcast_to<dimension_velocity> {};
```
2. Define the base unit (`std::ratio<1>`) and secondary ones and provide upcasting traits for them via:
2. Provide `quantity` class template partial specialization for new dimension and provide its base type:
```cpp
struct meter_per_second : unit<dimension_velocity, std::ratio<1>> {};
template<> struct upcasting_traits<upcast_from<meter_per_second>> : upcast_to<meter_per_second> {};
template<Unit U = struct meter_per_second, Number Rep = double>
using velocity = quantity<dimension_velocity, U, Rep>;
```
3. Define a concept that will match a new dimension:
```cpp
template<typename T>
concept Velocity = Quantity<T> && Same<typename T::dimension, dimension_velocity>;
concept Velocity = Quantity<T> && std::Same<typename T::dimension, dimension_velocity>;
```
4. Provide user-defined literals for the most important units:
4. Define the base and secondary units and provide upcasting traits for them:
```cpp
struct meter_per_second : derived_unit<dimension_velocity, meter, second> {};
template<> struct upcasting_traits<upcast_from<meter_per_second>> : upcast_to<meter_per_second> {};
struct kilometer_per_hour : derived_unit<dimension_velocity, kilometer, hour> {};
template<> struct upcasting_traits<upcast_from<kilometer_per_hour>> : upcast_to<kilometer_per_hour> {};
```
5. Provide user-defined literals for the most important units:
```cpp
inline namespace literals {
constexpr auto operator""_mps(unsigned long long l) { return velocity<meter_per_second, std::int64_t>(l); }
constexpr auto operator""_mps(long double l) { return velocity<meter_per_second, long double>(l); }
constexpr auto operator""_kmph(unsigned long long l) { return velocity<kilometer_per_hour, std::int64_t>(l); }
constexpr auto operator""_kmph(long double l) { return velocity<kilometer_per_hour, long double>(l); }
}
```
@@ -507,7 +521,7 @@ Additionally, it should make the error logs even shorter thus easier to understa
17. Should we leave `quantity` and specific dimensions as
```cpp
template<Dimension D, Unit U, Number Rep>
requires std::experimental::ranges::Same<D, typename U::dimension>
requires std::Same<D, typename U::dimension>
class quantity;
template<Unit U = meter_per_second, Number Rep = double>