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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: A bad counterintuitive behaviour of Ada about OO
Date: Fri, 8 Aug 2014 13:20:52 +0200
Organization: cbb software GmbH
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Date: 2014-08-08T13:20:52+02:00
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On Fri, 08 Aug 2014 05:10:25 -0600, Shark8 wrote:

> On 08-Aug-14 02:26, Dmitry A. Kazakov wrote:
>> The idea that subtyping can be directly reflect substitutability is the
>> root problem and the idea that the set of values could somehow define the
>> type so generalization or specialization might mean something. Ada's
>> subtypes suffer this as well. Both are wrong.
> 
> I don't understand this; subtypes are perfectly fine: essentially they 
> are subsets over the set of values that a type may take.

And they break in-operations. As an example consider:

   X : Integer := -1;

Now substitute Positive for Integer.

Subsetting means nothing to subtyping and both very little to
substitutability. All three are different things.

> -- Is this to say they are a magic bullet? Nope.

Huh, great mathematical problems are about fighting constraints. E.g.
solving x**n + y**n = z**n in real numbers vs. in natural ones. No big
deal? Same applies to programming, it is mostly about working around
constraints.

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