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From: dbc@cimage.com (David Caswell)
Newsgroups: comp.lang.eiffel,comp.object
Subject: Re: Inheritance and Information Hiding
Message-ID: <1991Feb8.154032.7277@cimage.com>
Date: 8 Feb 91 15:40:32 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> <1991Feb7.151212.25200@bony1.bony.com>
Reply-To: dbc@dgsi.UUCP (David Caswell)
Organization: Cimage Corp, Ann Arbor, MI
Lines: 13

.>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 don't think that we know how to add vertices to all POLYGONs.
Rectangles for example.  I think the solution is to put the 
rectangle methods on polygon and have them assert that the
number of vertices equals 4.  They could be put in another
file or whatever if you're worried about readability.  This 
problem comes up in countless situations.  Unfortunately
there is not a perfect solution.