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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Extending discriminant types
Date: Thu, 20 Nov 2008 16:29:00 -0800 (PST)
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Date: 2008-11-20T16:29:00-08:00
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On Nov 20, 2:59 pm, a...@anon.org (anon) wrote:
> First, the second specification package that I use was written by
> "Pascal Leroy". another editor of the Ada 2005 RM. "Randy Brukardt"
> skip this topic.
>
> QUOTE
> Our compiler currently rejects the following code fragment because it
> complains that the overriding "=" is not subtype conformant with the
> inherited "=" (3.9.2(10)):
>
>        package P is
>                 type T is tagged private;
>                 function "=" (Left, Right : T'Base) return Boolean;
>         private
>                 type T is tagged null record;
>         end P;
>
> T is a constrained subtype as per 3.2(9), so as far as I understand, T is
> different from the "T italic" used in 4.5.2(7).
>
> I hope that there is flaw in my reasoning, because if it is correct, it
> looks like we have a pretty severe problem...
>
> Pascal
> UNQUOTE
>
> And since both RM 95 and RM 2005, do not clarify that the "Base" attribute
> is for scalar types only, then you must assume that the "Base' attribute
> can apply to other types as well.

The Annotated Ada Reference Manual does clarify this, though.  See
AARM 3.5(63.a).  http://www.adaic.org/standards/05aarm/html/AA-3-5.html


 Else either "Pascal Leroy" or may be
> "Randy Brukardt" would have correct the misunderstanding of this
> attribute, especially since, Pascal implied the understanding in the
> first place by use of his example.

Either that, or both Pascal and Randy are human and both erred by
missing the problem.  It happens.

                                -- Adam