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.
Thanks to compile-time operations no runtime execution cost is introduced, facilitating the use of this library to provide dimension checking in performance-critical code. Support for quantities and units for arbitrary unit system models and arbitrary value types is provided, as is a fine-grained general facility for unit conversions.
The library architecture has been designed with flexibility and extensibility in mind. The demonstrations of the ease of adding new dimensions, their units, and unit conversions are provided in the Examples.
mp-units is Free and Open Source, with a permissive MIT license. Check out the source code and issue tracking (for questions and support, reporting bugs and suggesting feature requests and improvements) at https://github.com/mpusz/units.
Safety and performance
constexprall the things
as fast or even faster than when working with fundamental types
The best possible user experience
No macros in the user interface
No external dependencies
Possibility to be standardized as a freestanding part of the C++ Standard Library
With the User’s Experience in Mind
Most of the important design decisions in the library are dictated by the requirement of providing the best user experience as possible. Other C++ physical units libraries are “famous” for their huge error messages (one line of the error log often do not fit on one slide). The ultimate goal of mp-units is to improve this and make compile-time errors and debugging as easy and user-friendly as possible.
To achieve this goal several techniques are applied:
usage of C++20 concepts,
using strong types for framework entities (instead of type aliases),
limiting the number of template arguments to the bare minimum,
In many generic C++ libraries compile-time errors do not happen often. It is hard to
std::vector in a way it won’t compile with a huge error
log. Physical Units libraries are different. Generation of compile-time errors
is the main reason to create such a library.