forked from mpusz/mp-units
51 lines
4.9 KiB
Markdown
51 lines
4.9 KiB
Markdown
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# Introduction
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**mp-units** is a Modern C++ library that provides compile-time dimensional analysis and unit/quantity
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manipulation. The initial versions of the library were inspired by the
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[`std::chrono::duration`](https://en.cppreference.com/w/cpp/chrono/duration)
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but with each release, the interfaces diverged from the original to provide a better user
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experience.
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## Open Source
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**mp-units** is Free and Open Source, with a permissive
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[MIT license](https://github.com/mpusz/mp-units/blob/master/LICENSE.md). Check out the source
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code and issue tracking (for questions and support, reporting bugs, suggesting feature requests
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and improvements) at <https://github.com/mpusz/mp-units>.
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## With the User's Experience in Mind
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Most of the critical design decisions in the library are dictated by the requirement of
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providing the best user experience possible. Other C++ physical units libraries are
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"famous" for their enormous and hard-to-understand error messages (one line of the error log often
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do not fit on one slide). The ultimate goal of **mp-units** is to improve this and make compile-time
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errors and debugging as easy and user-friendly as possible.
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To achieve this goal, several techniques are applied:
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- usage of C++20 concepts,
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- using strong types for framework entities (instead of type aliases),
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- usage of expression templates to improve the readability of generated types,
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- limiting the number of template arguments to the bare minimum.
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!!! note
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In many generic C++ libraries compile-time errors do not happen often. It is hard to
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break `std::string` or `std::vector` in a way it won't compile with a huge error
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log. Physical Units libraries are different. **Generation of compile-time errors
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is the main reason to use such a library.**
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## Key Features
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| Feature | Description |
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|------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| **Safety** | - The affine space strong types (`quantity` and `quantity_point`)<br>- Compile-time checked conversions of quantities and units<br>- Unique support for many quantities of the same kind<br>- Type-safe equations on scalar, vector, and tensor quantities and their units<br>- Value-preserving conversions |
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| **Performance** | - All the compile-time logic implemented as immediate (`consteval`) functions<br>- As fast or even faster than working with fundamental types<br>- No space size overhead needed to implement high-level abstractions |
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| **Great User Experience** | - Optimized for readable compilation errors and great debugging experience<br>- Efficient and composable way to specify a unit of choice<br>- Value-based dimension, unit, and quantity equations |
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| **Feature Rich** | - Systems of Quantities<br>- Systems of Units<br>- Scalar, vector, and tensor quantities<br>- The affine space<br>- [Natural units systems](https://en.wikipedia.org/wiki/Natural_units) support<br>- Strong angular system<br>- Supports any unit's magnitude (huge, small, floating-point)<br>- Faster-than-lightspeed constants<br>- Highly adjustable text-output formatting |
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| **Easy to Extend** | - Each entity can be defined with a single line of code<br>- User can easily extend the systems with custom dimensions, quantities, and units |
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| **Low Standardization Cost** | - Small number of predefined entities needed thanks to composability<br>- No external dependencies (assuming full C++20 support)<br>- No macros in the user interface (besides portability and standard-compliance issues)<br>- Possibility to be standardized as a [freestanding](https://en.cppreference.com/w/cpp/freestanding) part of the C++ Standard Library |
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