Re: Unknown discriminants with nested records

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Simon Belmont <sbelmont700@gmail.com> writes:

> Thank you very much, that was the exact answer I was looking for.  I
> was supposing too much about the operation of the unknown discriminent
> marker; I figured it was more of a "known-but-I-won't-tell-you-because-
> you-don't-need-to-know" marker than an actual "unknown", and that the
> compiler would be able to determine that the record in question
> didn't, in fact, have any real discriminents.

If it worked that way, then it would break the contract on the private
type.  That is, you could make changes to the private part that would
affect the legality of clients.  Ada is designed to avoid that sort
of privacy breaking -- the content of the private part should never
affect the legality of any code outside that package.

Jeff Carter is correct about the original reason for the (<>) feature
-- to fix the generic contract model, which was broken in Ada 83.

- Bob