Re: [boost] [Review][PQS] Review deadline

From: David Greene (greened_at_[hidden])
Date: 2006-06-08 13:32:40

Andy Little wrote:

> Consider the calculation 1 km * 1 millisecond.
> 
> The external units approach
> 
> 1 * km * 1 * millisecond,
> which expanding the constants would be
> 
> 1 * 1000. * 1 * .001
> 
> In pqs the internal calculation at runtime is simply
> 
> 1. * 1.
> 
> The type of the result encodes the calculation  1000 * .001 as plus<3,-3>::value 
> in the unit of the result.

This, I think, is one of the great strengths of pqs.  The prefix is
encoded in the type system.  Now, Andy claims that this is why
prefix_offset is required.  I believe I understand his argument but
I'm not convinced yet.  I'll have to do some thinking on that.

I much prefer pqs' interface to conversion over the "external
conversion constants" system.  If I want to output something
in a particular unit, I'll create a pqs variable with the
appropriate unit and assign to it.

                           -Dave