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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: What would you like in Ada202X?
Date: Wed, 16 May 2012 09:39:50 +0200
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Date: 2012-05-16T09:39:50+02:00
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On Wed, 16 May 2012 00:35:30 +0300, Niklas Holsti wrote:

> I think that there are two quite different "use cases", from the user's 
> point of view, which correspond to "widening" and "deepening" 
> respectively. And I think that the "deepening" case is more worthy of 
> language support than the "widening" case.

There is narrowing too, presently handled though subtypes. You have type:

1. specialization (e.g. narrowing)
2. generalization (e.g. widening)
3. alternation (e.g. deepening)

Then you have two general models to bring types under one roof to have
objects of the class [*]:

1. subtypes + T'Base
2. separate types + T'Class

The rest is just details.

--------
* generic model lacks this property

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de