A C++20 library for descriptive units of measurements as drop-in replacements for fundamental types with minimal overhead.
- Static inheritance via C++20 concepts
- Implicit unit conversions
- Templated for arithmetic types
- Classes behave like fundamental types
constexpr auto IdealGas(int n, double V double T) -> double {
const auto R = 8.314;
const auto P = n * R * T / V;
return P;
}
constexpr void UseIG() {
const int n = 2;
const auto T = 300.0; // Units?
const auto V = 10.1; // Units?
auto pres = IdealGas(n,T,V); // No enforcement of incorrect parameter order
}#include <csm_units/units.hpp>
using namespace csm_units::literals;
constexpr auto IdealGas(csm_units::Kilomole n, csm_units::Liter V,
csm_units::Fahrenheit T) -> csm_units::Bar {
const auto R = 8.31446261815324 <<= m3 * Pa / K / mol;
// Using literals we can build what units the ideal gas constant R is using
// and assign that to the double.
// Conversion between units automatically occurs to ensure that arithmetic is
// following the rules set in place by the units. This can be seen below where
// R is Cubic Meter, Pascals, Kelvin, and Mole. While the arguments for the
// moles of the gas (n), volume, and temperature are in Kilomole, Liter, and
// Fahrenheit respectively. As well the answer is looking for Bar. All of the
// conversion happens behind the scene to ensure the answer is correct to Bar.
const csm_units::Bar P = n * R * T / V;
return P;
}
constexpr void UseIG() {
const auto n = csm_units::Mole(2);
const auto T = csm_units::Celsius(100.0);
const auto V = 10.1_m3; // string literal operators
// const auto pres = IdealGas(n,T,V); // Does not compile
const auto pres = IdealGas(n,V,T);
// The same auto converting happens when units are passed that are the same
// dimension, but different unit.
}| ns/op | benchmark |
|---|---|
| 0.54 | Add doubles |
| 0.52 | Add csm_units base units |
| 0.52 | Add csm_units derived units |
| 0.53 | Subtract doubles |
| 0.53 | Subtract csm_units base units |
| 0.52 | Subtract csm_units derived units |
| 0.52 | Multiply doubles |
| 0.52 | Multiply csm_units base units |
| 0.52 | Multiply csm_units derived units |
| 1.04 | Divide doubles |
| 1.04 | Divide csm_units base units |
| 1.04 | Divide csm_units derived units |