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