Re: orthogonal inheritance and extension aggregates

[Adam Beneschan <adambeneschan@aol.com>]

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:

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

This looks like a GNAT bug to me.

                                 -- Adam