Re: Extending discriminant types

[christoph.grein@eurocopter.com]

> Since I downloaded my binary version of GNAT-3.15p
> direct from Adacore. And someone else has said the GNAT-3.15p is old but
> it has been fully tested and found to be correct.
> So, that means that time Adacore agreed that "Base" attribute could be
> used outside of scalars and that was years after the RM and AARM for
> Ada 95 was written.

Having tested and delivered a compiler does by no means imply that
there are no bugs in it. Implying such a statement is silly. License
agreements take care of this.

> First, there is a  "interesting non-scalar attributes defined for an
> unconstrained composite or access subtype", it used in "Object-oriented
> programming" (OOP). But back in 90s, Ada was a late starter for OOP and
> even with the Ada 2005 OOP extensions some might still say its late to
> the plate or should that be table.

Ada was the first ISO standardized OO language (admittedly, there were
many OO languages before, but none standardized).

> Secondly, there is another side to 3.2.3 (8.a) and others listed in the
> AARM, and that is the clarifying statement "incompatibilities with Ada
> 83". But that does not say that "X'Base" or "T'Base" can not exist. If
> that was the case, a form of this statement would also be listed in
> "Annex J: Obsolescent Features" of the official RM.

Please see:
RM 1.1.1(6)  Permissible variations
   1.1.2(36) Implementation permissions
   1.1.3(6)  No variations

So there is nowhere a statement that 'Base may exist for other types.

Implementations may define other attributes, but they are not allowed
to use attribute names defined in the standard.

So please accept that if some compilers accept 'Base, this is a
mistake!