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From: <username>@most.fw.hac.com (<username>)
Subject: Re: Opinions on Ellipse-Circle dilemma?
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References: <5d4fmf$7gk@bagan.srce.hr> <u8rvi86ntcx.fsf@miris10.leeds.ac.uk> <32FA2A1C.6B31@arscorp.com> <E5B2HH.8AH@ecf.toronto.edu> <2367@purr.demon.co.uk>
Date: Tue, 11 Mar 1997 18:49:27 GMT
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Xref: glinda.oz.cs.cmu.edu comp.lang.c++:252872 comp.object:61969 comp.theory:18317 comp.lang.smalltalk:52746

In article <2367@purr.demon.co.uk>, jack@purr.demon.co.uk (Jack Campin) says:
>
>
>doylep@ecf.toronto.edu (Patrick Doyle) writes:
>> Norman Bunn  <bunn@arscorp.com> wrote:
>>> It has to do with sub-classing.  In other words...
>>> Is an ellipse as specialization of a circle (having two foci) or is a
>>> circle a specialization of an ellipse (having only one)?  Could we say
>>> in a circle's case, that it has two foci like the ellipse and they are
>>> just the same point?
>> Well, for my simplistic first impression, it seems to me that a circle
>> IS_A elipse, but an elipse is not a circle.  What are the arguments in
>> the other direction?  I'd descend circle from elipse.
>
>Imagine the thing's a mutable object in a drawing program.
>
>"elongate by a factor of 2 along the x axis" is a reasonable thing to ask
>an ellipse to do, but not a circle.  If Ellipse has behaviours that Circle
>doesn't, how can it be a superclass of Circle?  (without crude hacks).
>
>-----------------------------------------------------------------------------
>Jack Campin                                             jack@purr.demon.co.uk
>T/L, 2 Haddington Place, Edinburgh EH7 4AE, Scotland       (+44) 131 556 5272
>---------------------  Save Scunthorpe from Censorship  ---------------------
>

Do you have to one from another at all ? How about a Circle and an Ellipse 
which are both Shapes (or some other beastie) but not further related to 
one another !
