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Date: Mon, 03 Feb 2003 08:11:26 -0500
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: Anybody in US using ADA ? One silly idea..
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Dmitry A. Kazakov wrote:
> Yes, but in my why all this is same thing. Whether I write
> subtype X is Y <constraint>;
> or
> type X is new Y with <extension>;
> I produce a new type Y substitutable for X.

As your view conversion example showed, in the subtype case
we don't have a substitution but a two-way conversion. It
reminds me of school; the derived type is like a teacher who
has gone to graduate school and has come back with new degrees
while the subtype is like a substitute who fills in but doesn't
know very much.

> Isn't it strange, that 3 is available for methods, but not for data?

I still don't understand how you propose to inherit method
implementations while changing data representations.

> Consider a simplier approach.

I understand other approaches are possible, but as I keep saying,
those are not the approaches used in the conventional languages
which support OO, namely Ada, Java, C++, and probably Eiffel.
Ada experts do often use a style where an object containing
subobjects of type A, B, and C takes on the role of A, B, or C
as needed, in order to simulate multiple inheritance. Maybe you
can use something like that to do what you want?