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Newsgroups: comp.lang.ada
Date: Sun, 19 Jan 2020 20:32:44 -0800 (PST)
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Subject: Re: How to stop inheritance in a good way?
From: ric.wai88@gmail.com
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Xref: reader01.eternal-september.org comp.lang.ada:57902
Date: 2020-01-19T20:32:44-08:00
List-Id: <comp.lang.ada>

On Friday, January 17, 2020 at 8:39:59 AM UTC-5, Shark8 wrote:
> On Wednesday, January 15, 2020 at 1:32:14 AM UTC-7, reinert wrote:
> > 
> > and I want object2_2_t *not* to inherit the function B (from type object1_t).
> Well, there's two ways that you could do this:
> (1) If you don't need to pass the object to Object1_T'Class parameters or do inline view-conversions then simply make Object2_T a private type, copying over the interface you want to expose, with the inheritance in the full-view.
> (2) If you need to ensure that there is direct/visible inheritance, you could use generics and the "is null" default on functions to control behavior.
> 
> GENERIC
>   Type XX(<>) is abstract new Object2_T with private; -- You could use Int1_T.
>   with Function A_Implementation(X : XX) return Integer is null;
>   with Function B_Implementation(X : XX) return Integer is null;
>   --...
> Package Selective is
>   Type Child is new XX with null record;
> 
>   Overriding Function A( Object : Child ) return Integer;
>   --...
> Private
>   Function A( Object : Child ) return Integer is
>    ( A_Implementation(XX(Object)) );
>   --...
> End Selective;

Unfortunately you can't use "is null" on functions, only procedures..