RE: 2 Ada 95/05 language design questions

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

pnkflyd831@gmail.com writes:
> On Feb 15, 3:35 pm, Robert A Duff <bobd...@shell01.TheWorld.com>
> wrote:
...
> > One solution would be to have some syntax that means "this type might
> > have some private abstract operations, and therefore all derivations
> > from it must be in places where the full type is visible".  But I don't
> > think you want to treat ALL types that way.
> >
>
> Your absolutely correct.  My intent was not that all derived type
> linages must match the package lineage.  Additional syntax or the fact
> that the private abstract subprogram is still visible from the spec to
> the compiler and it could complain at compile time when you attempt to
> create a child that doesn't have the full type visible.

Additional syntax is OK. Making the legality of uses (in this case, derived
types) depend on the contents of the private part is not OK. Doing so breaks
encapsulation, in that a supposedly innocent change could cause all kinds of
unrelated code to fail.

I'm mildly surprised that you didn't mention the "no hidden interfaces" rule
of Ada 2007, because that seems to me to be much more problematic than
declaring a hidden abstract operation. OTOH, if you think of interfaces as
properties of a type (either a type has one or it does not; a type cannot
have one more than once), it makes more sense. But I've often thought that
I'm the only one with that particular model...

              Randy.