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Newsgroups: comp.lang.ada
Date: Fri, 19 Jul 2013 11:00:34 -0700 (PDT)
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Subject: Re: orthogonal inheritance and extension aggregates
From: Adam Beneschan <adambeneschan@aol.com>
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Xref: news.eternal-september.org comp.lang.ada:16433
Date: 2013-07-19T11:00:34-07:00
List-Id: <comp.lang.ada>

On Friday, July 19, 2013 10:46:38 AM UTC-7, Felix Krause wrote:
> I try to implement some feature via orthogonal inhertance like this:

>=20
>     generic
>        type Parent (<>) is abstract tagged private;
>     package Extension is
>        type Extended is abstract new Parent with private;
>=20
>        -- operations of the extended type here
>     private
>        type Extended is abstract new Parent with record
>           -- =85
>        end record;
>     end Extension;
>=20
> Now for testing, I tried to apply this on a Vector:
>=20
>     package Int_Vectors is new Ada.Container.Vectors (Natural, Integer);
>     package Base is new Extension (Int_Vectors.Vector);
>=20
>     type Child is new Base.Extended with null record;
>=20
>=20
> At the declaration of Child, GNAT tells me "type must be declared=20
> abstract or "To_Vector" overridden". Can someone explain why this=20
> happens? As I understand it, To_Vector should be automatically defined=20
> for the derived type. Is this because the intermediate type Extended is=
=20
> declared abstract? Or because To_Vector dispatches in the return type?

This looks like a GNAT bug to me.

                                 -- Adam