Re: Why should the value for a discriminant be static?

["Randy Brukardt" <randy@rrsoftware.com>]

"Jacob Sparre Andersen" <sparre@nbi.dk> wrote in message
news:rlszmyd956d.fsf@jacob.crs4.it...
> Occasionally I run into the limitation that the value for a
> discriminant be static.  I can design my way around the limitation
> (when I remember it), but I would like to know the reason.  (also
> because it might make it easier for me to remember the rule)

The only place I know of off-hand where there is such a limitation is with
aggregates. There, the limitation is necessary so that compiler can know the
set of components for the aggregate. Otherwise, it would be impossible to
check that components are given, which is *the* major benefit of using an
aggregate over a series of component assignments.

I suppose such a check could be done at runtime, but that would be
substantially less safe, as errors could exist in a program for a long time
and occur only in unusual conditions after deployment.

Anyway, does that answer your question, or was this in some other context?

                 Randy Brukardt