Re: [boost] [review] pqs

From: David Greene (greened_at_[hidden])
Date: 2006-06-08 13:40:53

Andy Little wrote:

> If kilograms played by the rules its exponent would be 3 , but for whatever 
> historical reasons its 0.

Why is "some historicasl reason" which we can't seem to puzzle out
driving the implementation of the library?

> The output for named quantities with coherent units is computed at compile time 
> from the class template signature.
> For those interested this is in:
> <boost/pqs/meta/components/adjusted_coherent_prefix.hpp>
> 
>  Without the prefix_offset, because kilograms has an exponent of 0, then its 
> unit output would be worked out as 'g', which is plainly wrong.
> 
> Does this help?

Why not just give kg anb exponent of "3" like everywhere else and then
adjust the other mass exponents accordingly.  Why special-case this?

>>AFAICT this has no impact on the user interface.  The user will
>>just specify pqs::mass::kg and doesn't care what the underlying
>>"prefix number" is.  But this change makes the framework extender's
>>job much easier.
> 
> 
> Complain to the SI people. It aint my fault guvnor!

But it's your library!  Honestly, I think you are too constrained
by some paper SI standard.  There is nothing at all that says
the library must be implemented this way.

                              -Dave