Re: Dimensionality Checking (Ada 20XX)

["Mark Lundquist" <mlundquist2@attbi.com>]

"Wes Groleau" <wgroleau@usa.com> wrote in message
news:3C0FF376.2DC0C3E4@usa.com...
>
>
> Britt Snodgrass wrote:
> > (dimensionality) in Ada code would be most naturally implemented as
> > attributes of objects or types.  The units of an object or type would
> > be specified with a representation clause.  If unspecified, the unit
>
> I think this is a very good idea.  But now to nitpick:
>
> >    Accel : Magnitude;
> >    for Accel'Unit use
> >      ISO_Metric_Units.Meter / ISO_Metric_Units.Second**2;
>
> In some cases, might there be multiple ways to describe
> the units?   Speed is Acceleration * Time but it is also
> Distance / Time.

Right, which is why (a) the concepts of "unit" and of "dimension" need to be
loosely coupled (this is missing from the proposals I've seen so far), and
then (b) you have to distinguish between base and derived dimensions.

We normally think of Distance and Time as being "fundamental", so typically
we would declare these as base dimensions.  Then we declare the derived
dimension Rate = Distance / Time.  That's (a).

(b) says that Rate = Distance / Time no matter the units.

The dimensionality checking would be done in terms of base dimensions, so it
makes no difference "how you got there", e.g. in terms of derived
dimensions.

Best Regards,
Mark