forked from mpusz/mp-units
Mateusz Pusz
9527b39005
We had some fun exploring the STD UDLs for potential collisions, we have learnt our lesson and know how to proceed. Now is high time to start behaving and obeying C++ rules.
84 lines
3.2 KiB
Markdown
84 lines
3.2 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(10_q_km / 2 == 5_q_km);
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// unit conversions
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static_assert(1_q_h == 3600_q_s);
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static_assert(1_q_km + 1_q_m == 1001_q_m);
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// dimension conversions
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static_assert(1_q_km / 1_q_s == 1000_q_m_per_s);
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static_assert(2_q_km_per_h * 2_q_h == 4_q_km);
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static_assert(2_q_km / 2_q_km_per_h == 1_q_h);
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static_assert(2_q_m * 3_q_m == 6_q_m2);
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static_assert(10_q_km / 5_q_km == 2);
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static_assert(1000 / 1_q_s == 1_q_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 <units/format.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(220_q_km, 2_q_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 << fmt::format("{}", v2) << '\n'; // 70 mi/h
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std::cout << fmt::format("{:%Q in %q}", v3) << '\n'; // 31.2928 in m/s
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std::cout << fmt::format("{:%Q}", v4) << '\n'; // 31
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}
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```
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_Try it on the [Compiler Explorer](https://godbolt.org/z/xE91TY)._
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