From mboxrd@z Thu Jan  1 00:00:00 1970
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From: Robert A Duff <bobduff@world.std.com>
Subject: Re: OO puzzle
Date: 1999/12/23
Message-ID: <wccr9gdaefw.fsf@world.std.com>#1/1
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Sender: bobduff@world.std.com (Robert A Duff)
References: 
 <Pine.A41.3.96-heb-2.07.991222103646.28794B-100000@pluto.mscc.huji.ac.il>
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Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 1999-12-23T00:00:00+00:00
List-Id: <comp.lang.ada>

Ehud Lamm <mslamm@mscc.huji.ac.il> writes:

> But than you lose the ability to define the abstract interface (for
> Motor_Vehicle) and know that it is supported by all descendants.

But it seems to me that you are *not* requiring the descendants to
support that interface.  You are trying to let the descendants support a
different operation, also called "register", but with a different
contract (ie, trucks can't register airplane drivers, although the
parent type implied they could -- or whatever the example was).

It's an interesting language design issue, anyway.

- Bob