forked from mpusz/mp-units
107 lines
4.5 KiB
Markdown
107 lines
4.5 KiB
Markdown
[](./LICENSE.md)
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[](https://github.com/mpusz/units/actions?query=workflow%3A%22Conan%20CI%22+branch%3Amaster)
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[](https://github.com/mpusz/units/actions?query=workflow%3A%22CMake+Test+Package+CI%22+branch%3Amaster)
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[](https://github.com/mpusz/units/actions?query=workflow%3ADocumentation+branch%3Amaster)
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[](https://bintray.com/mpusz/conan-mpusz/mp-units%3Ampusz/0.6.0%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 ISO standardization for C++23/26. More on this can
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be found in ISO C++ paper [P1935](https://wg21.link/p1935) and
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[CppCon 2020 talk](https://www.youtube.com/watch?v=7dExYGSOJzo). We are actively looking for
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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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#include <units/isq/si/area.h>
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#include <units/isq/si/frequency.h>
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#include <units/isq/si/length.h>
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#include <units/isq/si/speed.h>
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#include <units/isq/si/time.h>
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using namespace units::isq::si::references;
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// simple numeric operations
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static_assert(10 * km / 2 == 5 * km);
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// unit conversions
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static_assert(1 * h == 3600 * s);
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static_assert(1 * km + 1 * m == 1001 * m);
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// dimension conversions
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inline constexpr auto kmph = km / h;
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static_assert(1 * km / (1 * s) == 1000 * (m / s));
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static_assert(2 * kmph * (2 * h) == 4 * km);
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static_assert(2 * km / (2 * kmph) == 1 * h);
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static_assert(2 * m * (3 * m) == 6 * m2);
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static_assert(10 * km / (5 * km) == 2);
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static_assert(1000 / (1 * s) == 1 * kHz);
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```
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_Try it on the [Compiler Explorer](https://godbolt.org/z/ToTaoxKPa)._
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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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#define UNITS_UDLS 1
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#include <units/format.h>
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#include <units/isq/si/length.h>
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#include <units/isq/si/speed.h>
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#include <units/isq/si/time.h>
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#include <units/isq/si/international/length.h>
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#include <units/isq/si/international/speed.h>
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#include <units/quantity_io.h>
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#include <iostream>
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using namespace units::isq;
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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::isq::si::literals;
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using namespace units::isq::si::references;
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constexpr Speed auto v1 = 110 * (km / h);
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constexpr Speed auto v2 = avg_speed(220_q_km, 2_q_h);
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constexpr Speed auto v3 = avg_speed(si::length<si::international::mile>(140), si::time<si::hour>(2));
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constexpr Speed auto v4 = units::quantity_cast<si::speed<si::metre_per_second>>(v2);
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constexpr Speed auto v5 = units::quantity_cast<si::metre_per_second>(v3);
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constexpr Speed auto v6 = units::quantity_cast<int>(v5);
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std::cout << v1 << '\n'; // 110 km/h
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std::cout << fmt::format("{}", v2) << '\n'; // 110 km/h
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std::cout << fmt::format("{:*^14}", v3) << '\n'; // ***70 mi/h****
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std::cout << fmt::format("{:%Q in %q}", v4) << '\n'; // 30.5556 in m/s
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std::cout << fmt::format("{0:%Q} in {0:%q}", v5) << '\n'; // 31.2928 in m/s
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std::cout << fmt::format("{:%Q}", v6) << '\n'; // 31
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}
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```
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_Try it on the [Compiler Explorer](https://godbolt.org/z/YodshMKac)._
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