Xref: utzoo comp.lang.eiffel:1387 comp.object:2526
Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!bony1!richieb
From: richieb@bony1.bony.com (Richard Bielak)
Newsgroups: comp.lang.eiffel,comp.object
Subject: Re: Inheritance and Information Hiding
Message-ID: <1991Feb7.151212.25200@bony1.bony.com>
Date: 7 Feb 91 15:12:12 GMT
References: <488@eiffel.UUCP> <27A86309.281A@tct.uucp> <1991Feb1.135956.12425@tukki.jyu.fi> <27ADD06B.46A3@tct.uucp> <1991Feb5.130359.9735@bellcore.bellcore.com> <1991Feb6.045542.791@visix.com>
Reply-To: richieb@bony1.UUCP (Richard Bielak)
Organization: Bank of New York
Lines: 33

In article <1991Feb6.045542.791@visix.com> adam@visix.com (Adam Kao) writes:
>
[...lots of stuff deleted...]

>We know how to add vertices to POLYGONs.  I think it ridiculous to say
>we do not know how to add vertices to RECTANGLEs.  The problem is,
>adding a vertex to a RECTANGLE gives us something that is not a
>RECTANGLE.  
>
>I do not see this as a problem.  Why do we expect that all operations
>on an Object must be closed over its Class?
>

Perhaps the "add_vertex" routine should be a function? How about
this:

       add_vertex : POLYGON is
                do
                        -- whatever
                end;


Then if "r" is a RECTANGLE, we can call "r.add_vertex" and get back
an object that is not a RECTANGLE.



...richie
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