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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Is the Writing on the Wall for Ada?
Date: Wed, 24 Sep 2003 14:55:03 +0200
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Date: 2003-09-24T14:55:03+02:00
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On Wed, 24 Sep 2003 11:43:08 GMT, Matthew Heaney
<matthewjheaney@earthlink.net> wrote:

>Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> writes:
>
>> T_Set and NT_Set are unrelated types. So one cannot be a
>> subtype/subclass of another. It means that I cannot write a
>> NON-GENERIC program operating on both.
>
>Your problem was to have an operation to traverse a container of
>Element_Type, and to be able to reuse the same operation over a
>container whose element type derives from Element_Type.
>
>The solution I showed does that.  Whether it's generic vs. non-generic
>shouldn't matter.

It matters, because generics cannot be put into a library, because
they need to be instantiated. The solution is unhandy and too complex.
What I need is a quite simple and understandable thing. I want to take
a container type and put a constraint on it. In terms of
discriminants:

   -- This is not Ada!
type Container (Element_Tag : T_Set'Class'Tag) is ...;
subtype Specialized_Container is Container (NT_Set'Class'Tag);

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de