forked from mpusz/mp-units
120 lines
5.6 KiB
Markdown
120 lines
5.6 KiB
Markdown
[](./LICENSE.md)
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[](https://en.cppreference.com/w/cpp/compiler_support#cpp20)
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[](https://github.com/mpusz/mp-units/actions?query=workflow%3A%22Conan%20CI%22+branch%3Amaster)
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[](https://github.com/mpusz/mp-units/actions?query=workflow%3A%22CMake+Test+Package+CI%22+branch%3Amaster)
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[](https://github.com/mpusz/mp-units/actions?query=workflow%3A%22Check%20CI%22+branch%3Amaster)
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[](https://github.com/mpusz/mp-units/actions?query=workflow%3ADocumentation+branch%3Amaster)
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[](https://conan.io/center/mp-units)
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[](https://mpusz.jfrog.io/ui/packages/conan:%2F%2Fmp-units/2.0.0)
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# `mp-units` - A Physical Quantities and Units library for C++
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**The mp-units library might be the subject of ISO standardization for C++29.
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More on this can be found in ISO C++ paper [P1935](https://wg21.link/p1935) and
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[Using std::cpp 2023 talk](https://www.youtube.com/watch?v=3XSVCmWQklI).
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We are actively looking for parties interested in field trialing the library.**
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[](https://gitpod.io/#https://github.com/mpusz/mp-units)
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**NOTE: The master branch right now is under heavy development of the V2 framework.
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For now it compiles only on gcc-12+. In the upcoming months a lot of efforts will be done to
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enable the rest of mainstream compilers and update the documentation to reflect the V2 design.**
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## Documentation
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An extensive project documentation for the previous release library version can be found on
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[mp-units GitHub Pages](https://mpusz.github.io/mp-units). It includes installation instructions and user's guide.
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## Terms and Definitions
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This project uses the official metrology vocabulary defined by the ISO and BIPM.
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Please familiarize yourself with those terms to better understand the documentation
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and improve domain-related communication and discussions. You can find essential
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project-related definitions in [our documentation's "Glossary" chapter](https://mpusz.github.io/mp-units/glossary.html).
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Even more terms are provided in the official vocabulary of the [ISO](https://www.iso.org/obp/ui#iso:std:iso-iec:guide:99:ed-1:v2:en)
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and [BIPM](https://jcgm.bipm.org/vim/en).
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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.
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Here is a small example of possible operations:
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```cpp
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#include <mp-units/systems/si/si.h>
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using namespace mp_units::si::unit_symbols;
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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/j8afKnarv)._
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This library heavily uses C++20 features (concepts, classes as NTTPs, ...). Thanks to
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them the user gets a powerful but still easy to use interfaces and all unit conversions
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and dimensional analysis can be performed without sacrificing on runtime performance or
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accuracy. Please see the below example for a quick preview of basic library features:
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```cpp
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#include <mp-units/format.h>
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#include <mp-units/iostream.h>
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#include <mp-units/systems/international/international.h>
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#include <mp-units/systems/isq/space_and_time.h>
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#include <mp-units/systems/si/si.h>
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#include <iostream>
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using namespace mp_units;
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constexpr QuantityOf<isq::speed> auto avg_speed(QuantityOf<isq::length> auto d,
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QuantityOf<isq::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 mp_units::si::unit_symbols;
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using namespace mp_units::international::unit_symbols;
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constexpr auto v1 = 110 * (km / h);
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constexpr auto v2 = 70 * mph;
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constexpr auto v3 = avg_speed(220. * km, 2 * h);
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constexpr auto v4 = avg_speed(isq::distance(140. * mi), 2 * isq::duration[h]);
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constexpr auto v5 = v3[m / s];
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constexpr auto v6 = value_cast<m / s>(v4);
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constexpr auto v7 = value_cast<int>(v6);
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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 << std::format("{}", v3) << '\n'; // 110 km/h
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std::cout << std::format("{:*^14}", v4) << '\n'; // ***70 mi/h****
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std::cout << std::format("{:%Q in %q}", v5) << '\n'; // 30.5556 in m/s
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std::cout << std::format("{0:%Q} in {0:%q}", v6) << '\n'; // 31.2928 in m/s
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std::cout << std::format("{:%Q}", v7) << '\n'; // 31
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}
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```
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_Try it on the [Compiler Explorer](https://godbolt.org/z/rrTojn47v)._
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