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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: generic question
Newsgroups: comp.lang.ada
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Date: Tue, 21 Nov 2006 19:28:59 +0100
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Date: 2006-11-21T19:28:52+01:00
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On 21 Nov 2006 10:15:42 -0800, Matthew Heaney wrote:

> So that conversions towards the root of a tagged type hierarchy don't
> require explicit type conversions.

True, but it is only because there is no subtypes of access types like:

type T is tagged ...;
type T_Ptr is access T'Class;

type S is new T with ...;
subtype S_Ptr is T_Ptr in S'Class;

In the present design three uncorrelated things are bundled together in
anonymous access types:

1. subtypes hierarchy inherited from the target types hierarchy
2. general pool
3. controlledness in primitive subprograms

In Ada 95 it was even four:

4. not null

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