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Date: Mon, 03 Feb 2003 08:26:33 -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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Date: 2003-02-03T08:26:33-05:00
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Dmitry A. Kazakov wrote:
> Then you should explain what "is a" does mean. It is definitely not
> mathematical =, as memcpy shows.

Memcpy is not a "mathematical =" but a procedure which copies
a bunch of bytes in memory. You won't like my explanation of
"is a" becuase it's purely practical - "B is a A" means that
a pointer or reference to A may hold a pointer or reference to
an object of type B (or a type which "is a B") and may call
methods of A using that pointer or reference.

> If you define a type, say, "field".

But we are not talking about defining a type, but about
defining a procedure. This procedure defines an interface
implicitly by virtue of the operations it uses. You then
claim that this implicit interface needs to be augmented
with operations that the procedure doesn't need, and then
that types upon which the procedure operates need to have
these useless operations, and that this somehow achieves
safety! I am just baffled.