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From: Keith Nicewarner (Keith.Nicewarner_at_[hidden])
Date: 2005-11-14 00:36:38

Geoffrey Romer wrote:
> Would there be any interest in a library for attaching units (physical
> or otherwise) to numeric variables, so that the type system could
> enforce dimension- and unit-consistency in all calculations, and
> convert semi-automatically between compatible units?

I'm fairly new to boost, so forgive my late entry into this discussion. I too recognized the need for this kind of library back in the late 90s and wrote this library available on SourceForge:

It's pretty stable and used on several projects (there's a military simulation tool that has standardized on it). I've recently discovered the meta-programming method for dimensional quantities by Scott Meyers:

This inspired me to revisit my library and it is turning out to be a fairly easy conversion. The old library had to explicitly represent each unit combination of interest (e.g., Speed = Length/Time), which is ugly and doesn't allow arbitrary combinations. The new method fixes all this (in fact, it simplifies things to the point where there is no library object file any more -- just headers).

A key concept I tried to enforce is that any time the programmer sets or gets a numeric value, the specific units (i.e., Feet, Meters, etc.) must be specified. I don't want any units to be implicit. My library provides ostream formatting for handy printing. I also provide scalar, 2D, and 3D types. For the 2D/3D types, I provide various transformation operators like rotation. For 3D rotations, I provide the option of cosine matrix or unit quaternion.

It's been suggested to me that I submit my library to boost. Being new to boost, I'm not sure how complete and tested the code needs to be. Any feedback or suggestions are welcome.



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