Re: [boost] formal review request : mcs::units

From: Deane Yang (deane_yang_at_[hidden])
Date: 2007-02-10 20:29:00

Michael Marcin wrote:
> Matthias Schabel wrote:
>> Hi Michael,
>>
>>> When working in 3d simulations it is necessary to transform vectors to
>>> different spaces.  Bugs sometimes crop up when, for instance, adding a
>>> object space vector to a world space vector or adding a vector from
>>> object a's object space to one from object b's object space.  It would
>>> be nice to catch such inconsistencies at compile-time.  I have a  
>>> feeling
>>> a units-like library would be able to handle this but I have no  
>>> idea how
>>> it would work.
>> Here are two ways to do it, with the quantity wrapping the vector or the
>> vector containing quantities:
>>
>> <snip>
>>
> 
> That's pretty cool and would likely catch many of the problems.  The 
> other error cases seem harder to detect at compile time.  At least for 
> my purposes there is only one world space but there can be an arbitrary 
> number of object spaces.  In addition it can be difficult to define 
> correct conversions between spaces.
> 
><snip>

If you think about it, you begin to realize that in *all* code involving 
arithmetic calculations (not just in physics or finance), you should 
wrap virtually every double with a type and define allowable operations 
using those types. This would catch a lot of errors at compile time.