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From: dmitry@elros.cbb-automation.de (Dmitry A. Kazakov)
Newsgroups: comp.lang.ada
Subject: Re: How to avoid unreferenced objects (mutexes etc)
Date: Thu, 17 Jan 2002 10:42:30 GMT
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Date: 2002-01-17T10:42:30+00:00
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On Thu, 17 Jan 2002 09:19:59 +0000 (UTC), lutz@iks-jena.de (Lutz
Donnerhacke) wrote:

>* Dmitry A. Kazakov wrote:
>>I believe it is worth to allow that for all types, i.e. to allow
>>overriding a non-abstract subroutine with an abstract one. A
>>dispatching call to a disallowed subprogram will then raise an
>>exception [like when tags of arguments are different].
>
>I strongly discourage from such a change. Class wide programming using
>abstract tagged types are used for the guarantee of a working interface.

There is no way to enforce LSP, if you aim at that. Just consider an
overriding like:

procedure Do_Something (...) is
begin
   raise Program_Error;
end Do_Something;

And who said that derived types shall be LSP subtypes? What should we
do with

subtype Positive ...;

then?

Regards,
Dmitry Kazakov