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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Preventing type extensions
Newsgroups: comp.lang.ada
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Date: Mon, 13 Sep 2010 09:13:43 +0200
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Date: 2010-09-13T09:13:40+02:00
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On Mon, 13 Sep 2010 07:32:02 +0200, Florian Weimer wrote:

> * Maciej Sobczak:
> 
>> If it implements an abstract interface, then why extending it further
>> is a problem? From the user point of view (that is, from the point of
>> view of the subprogram that accepts Some_Interface'Class and operates
>> on it), it does not matter how deep is the hierarchy.
> 
> Type extensions break encapsulation (at least if there non-abstract
> dispatching subprograms which contain some non-trivial code): the
> information which subprograms call each other under what circumstances
> leaks to the outside of the package. One very drastic way to
> implement that is to disallow type extensions for most non-abstract
> types you write, and consider the exceptions carefully.

No, the actual problem here is re-dispatch. Just do not do that, it is
always bad.

Final classes make no sense. I am glad that at least this was not borrowed
by Ada ... yet.

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