forked from mpusz/mp-units
83 lines
3.0 KiB
Markdown
83 lines
3.0 KiB
Markdown
[](./LICENSE.md)
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[](https://travis-ci.com/mpusz/units)
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[](https://bintray.com/mpusz/conan-mpusz/mp-units%3Ampusz/0.5.0%3Astable/link)
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[](https://bintray.com/mpusz/conan-mpusz/mp-units%3Ampusz/_latestVersion)
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# `mp-units` - A Units Library for C++
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**The mp-units library is the subject of this ISO C++ paper: [P1935](https://wg21.link/p1935).
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It is explained in this [CppCon 2019 talk](https://youtu.be/0YW6yxkdhlU) (slightly dated now).
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We are working towards potentially having it standardized for C++23 and are actively looking
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for parties interested in field trialing the library.**
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## Documentation
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An extensive project documentation including installation instructions and user's
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guide can be found on [mp-units GitHub Pages](https://mpusz.github.io/units).
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## TL;DR
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`mp-units` is a compile-time enabled Modern C++ library that provides compile-time dimensional
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analysis and unit/quantity manipulation. The basic idea and design heavily bases on
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`std::chrono::duration` and extends it to work properly with many dimensions.
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Here is a small example of possible operations:
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```cpp
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// simple numeric operations
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static_assert(10q_km / 2 == 5q_km);
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// unit conversions
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static_assert(1q_h == 3600q_s);
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static_assert(1q_km + 1q_m == 1001q_m);
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// dimension conversions
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static_assert(1q_km / 1q_s == 1000q_m_per_s);
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static_assert(2q_km_per_h * 2q_h == 4q_km);
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static_assert(2q_km / 2q_km_per_h == 1q_h);
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static_assert(2q_m * 3q_m == 6q_m2);
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static_assert(10q_km / 5q_km == 2);
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static_assert(1000 / 1q_s == 1q_kHz);
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```
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_Try it on the [Compiler Explorer](https://godbolt.org/z/XPmjPz)._
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This library requires some C++20 features (concepts, classes as NTTPs, ...). Thanks to
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them the user gets a powerful but still easy to use interface and all unit conversions
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and dimensional analysis can be performed without sacrificing on accuracy. Please see
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the below example for a quick preview of basic library features:
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```cpp
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#include <units/physical/si/speed.h>
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#include <units/physical/international/speed.h>
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#include <iostream>
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using namespace units::physical;
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constexpr Speed auto avg_speed(Length auto d, Time auto t)
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{
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return d / t;
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}
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int main()
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{
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using namespace units::physical::si::literals;
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Speed auto v1 = avg_speed(220q_km, 2q_h);
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Speed auto v2 = avg_speed(si::length<international::mile>(140), si::time<si::hour>(2));
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Speed auto v3 = quantity_cast<si::metre_per_second>(v2);
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Speed auto v4 = quantity_cast<int>(v3);
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std::cout << v1 << '\n'; // 110 km/h
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std::cout << v2 << '\n'; // 70 mi/h
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std::cout << v3 << '\n'; // 31.2928 m/s
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std::cout << v4 << '\n'; // 31 m/s
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}
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```
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_Try it on the [Compiler Explorer](https://godbolt.org/z/f-f6y6)._
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