Summary
Various musings about how to deal with units of measure in the Heron graphics library.

I am [hopefully] laying the foundation for the standard graphical library for Heron and I have been learning about Scalable Vector Graphics (SVG). I am trying to keep my fingers on the pulses of various technologies in order to ensure easy interoperability. For instance, it would be nice if the various primitive drawing functions could be done just as easily to a bitmap, as to an SVG file.

Anyway, that said, one thing I notice about SVG, HTML, CSS, etc., is that they usually support multiple units of measure: pixels, cm, inches, points, and percent. Most library API's I am familiar with only give one option: pixels. This raises some of the following questions:

• Is it truly desirable to support multiple units of measure?
• Is it reasonable to expect units of measure to be mixed: i.e. point(pixels(24), percent(50))
• Should I introduce new types for each unit of measure?
• Should I try and modify the language grammar so that syntax like: point(24 pixels, 50 percent) was legal?
• If I did allow units of measure in a natural syntax would that mean the expression: value unit means unit(value)?
• In the above example is unit a type or a function (or both)?
• If value type meant type(value), wouldn't it be logical to completely remove type(value) type-casting syntax to avoid confusion?

I am only scratching the surface of the topic of units of measure. In physics units of measure are a very big deal. For those interested in further exploring the topic of units of measure as types, here are some related links:

• Andrew Kennedy: Publications on Units of Measure, specifically his introduction is intriguing.
• Representing Dimensions, discusses a Template Metaprogramming approach to the problem of units of measure in C++.
• Frink is a programming language which specializes in dealing with units of measure.
• Measure Twice, Cut Once - Discusses the basic concepts and issues pertaining to representing units of measure in code

As usual, any ideas or suggestions are most welcome.

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About the Blogger

Christopher Diggins is a software developer and freelance writer. Christopher loves programming, but is eternally frustrated by the shortcomings of modern programming languages. As would any reasonable person in his shoes, he decided to quit his day job to write his own ( www.heron-language.com ). Christopher is the co-author of the C++ Cookbook from O'Reilly. Christopher can be reached through his home page at www.cdiggins.com.