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RATIONALE.md

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Rationale

This library is a result of my experiments with Scala's type system.

The goal I was aiming for when working on this library was to provide units of measurement with following properties:

  • values with units are unboxed (possible thanks to Scala 2.10's custom value classes)

  • units can be defined by user (as opposed to implementations limiting users to seven base SI units)

  • all unit checking should be done on compile time (as opposed to runtime)

  • not a compiler plugin or a macro (although I may add some macro-powered syntactic sugar in the future)

  • proper support for affine spaces

  • easy conversion between units

Why not any other implementation?

All of the following implementations were either inefficient or inflexible:

  • units (compiler plugin)

    • Both outdated and a compiler plugin.

  • Metascala Units

  • scalax-units

  • ScalaQuantity

    • All three above are limited to 7 SI units only, and since they were made before 2.10, values are boxed. They were the direct inspiration for this library.

  • axle.quanta

    • Allows for adding new units, but all unit checking is performed at runtime, causing a significant runtime overhead.

  • scalau

    • A source code preprocessor. Converts all units to SI. Does not support arbitrary unit expressions, for example metre to the fourth power would be an invalid unit.