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Date: Thu, 07 Sep 2006 08:48:21 +0200
From: Georg Bauhaus <bauhaus@futureapps.de>
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Subject: Re: Generic procedures and their parameters
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Date: 2006-09-07T10:46:59+02:00
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Dmitry A. Kazakov wrote:

> But this all is independent on the question whether interface and
> implementation inheritances are different things. They are not. 

Suppose I have some complex number type C
having a lengthy division operation that requires
auxiliary components in the implementation.

Now I want a type of complex numbers just like C
but without a division operation.
One way to do so might seem to inherit a D from C,
and clear the division operation,

   type C is tagged private;
   ...
   procedure division(a, b: C; result: in out C);


   type D is new C with private;
   ...
   overriding
   procedure division(a, b: D; result: in out D) is null;

(Is there anything better than null BTW? It won't remove
division from D's interface...)
This will leave the auxiliary components of C in D.

But couldn't I do better? For example, by declaring
the interface I want, and then requesting that the needed
operations be "extracted" from C, dropping the division
stuff (provided there is a way to mark components as being
needed by only some set of operations.)

I will loose view conversions to C.
But if that is what I want? Just a composition of
the interface I need in some scope?