mp-units - A Units Library for C++

Summary

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(10_km / 2 == 5_km);

// unit conversions
static_assert(1_h == 3600_s);
static_assert(1_km + 1_m == 1001_m);

// dimension conversions
static_assert(1_km / 1_s == 1000_mps);
static_assert(2_kmph * 2_h == 4_km);
static_assert(2_km / 2_kmph == 1_h);

static_assert(1000 / 1_s == 1_kHz);

static_assert(10_km / 5_km == 2);

Repository structure

That repository contains the following independent cmake-based projects:

• ./src - header-only project for units
• . - project used for development needs that wraps ./src project together with usage examples and unit tests
• ./test_package - library installation and Conan package verification

Please note that the projects depend on cmake git submodule in the ./cmake/common subdirectory.

Building, testing, and installation

For a detailed information on project compilation, testing and reuse please refer to doc/INSTALL.md.

NOTE: This library as of now compiles correctly only with gcc-9.1 and newer.

Library design

units library design rationale and documentation can be found in doc/DESIGN.md

Release notes

• 0.3.1 Sep 18, 2019

  • cmcstl2 dependency changed to range-v3 0.9.1

• 0.3.0 Sep 16, 2019 (CppCon 2019 design)

  • The design as described on CppCon 2019 talk
  • Applied the feedback from the Cologne evening session
    • upcasting_traits renamed to downcasting_traits
    • Dimension template parameter removed from quantity
  • units moved to a std::experimental namespace
  • Leading underscore prefix removed from UDLs
  • Added a few more derived dimensions
  • meter renamed to metre
  • Missing operator* added
  • Predefined dimensions moved to a dedicated directory
  • dimension_ prefix removed from names of derived dimensions
  • cmcstl2 library updated to 2019.09.19
  • base_dimension is a value provided as const& to the exp type
  • integrated with Compiler Explorer
  • gsl-lite deppendency removed
  • Fractional dimension exponents support added
  • QuantityOf concept introduced
  • quantity_cast<U, Rep>() support added

• 0.2.0 July 18, 2019 (C++Now 2019 design)

  • The design as described on C++Now 2019 talk (https://youtu.be/wKchCktZPHU)
  • Added C++20 features supported by gcc-9.1 (std::remove_cvref_t, down with typename, std::type_identity)
  • Compile-time performance optimisations (type_list, common_ratio, ratio, conditional_t)

• 0.1.0 May 18, 2019

  • Initial library release
  • Begin semantic versioning
  • The last version to work with gcc-8