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Subject: Re: [office-comment] Re: Unit system tracking

Alex Hudson:
>I think that's a bit of a hostage to fortune: essentially, we're talking about typed data (in CS-speak), and if the other side isn't typed then automated conversion into the typed format is obviously impossible...

Unit systems are "typed" in a broad sense, but are RADICALLY different than "normal" type systems that most programming languages support.  For example, new types are constantly created at run-time on the fly (e.g., divide "meter" by "second" and they expect the result to be "m/s").  There many type name aliases (like "Newton").  Conversion factors aren't just powers of 10 (centimeter/inch), aren't just multiplicative (Celcius/Fahrenheit), and aren't always constant or reciprocal (Euro/U.S. Dollar).

There's a lot of experience in the Ada community on this very topic.  Ada has very good strong typing support for "traditional" data types, but when people tried to create types like "meters_squared" they soon discovered that the "obvious" type systems DO NOT WORK when handling unit systems in most cases.  Eventually they had to create complex overheads to track the units.

>The typed stuff is extra mojo on top. While it doesn't aid conversion, I don't see that it hampers it.

If you have to keep track _AT ALL_ then you have to ALWAYS be prepared for it.

>I probably mostly agree with the end decision, but I think this should be kept on the radar. 

Agree.  This is a _good_ idea, but will require real effort to bring to fruition.   Perhaps once we wrap up this stage, someone will be willing to champion it, including investing the time it will take.

--- David A. Wheeler

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