Path: news.daimi.aau.dk!jlk
From: jlk@daimi.aau.dk (Jorgen Lindskov Knudsen)
Newsgroups: comp.lang.beta
Subject: Re: Ellipse Circle dilemma?
Date: 3 Mar 1997 21:38:53 GMT
Organization: DAIMI, Computer Science Dept. at Aarhus University
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In <5fefm5$2ok@bagan.srce.hr> kmajor@jagor.srce.hr (Kazimir Majorinc) writes:

>Hi!

>I did not get any answer about this - maybe my newserver is 
>wrong. I'd like to hear how will you do it in Beta.

>In C++ problem is that CIrcle can not be inherited from Ellipse
>because Circle::SetXYAxes(1,2) is defined. It seems there is no
>good solution in C++.

>class Ellipse { float a,b;
>                float Area(){return a*b*3.145;}
>                void SetXYAxes(float x0,float y0);
>               };
>class Circle::public Ellipse{// something ...
>                             };

>Now we have Circle::SetXYAxes(1,2)

>So, what's your best design of relation between Circle and Ellipse in Beta.
>This is important!

With insistence on the above hierarchy, I don't thing, that BETA
offers any more elegant solution.

However, we can rearrange the hierarchy to reflect the intended
semantics, which is, that ellipsis and circle are closed curves with
an area:

closedCurve:
  (# area:< (# a: @real do INNER exit a #);
  #);

ellipse: closedCurve
  (# a,b: @real;
     setXYaxes: (# enter (a,b) #);
     area::< (# do a*b*3.145->a #);
  #);

circle: closedCurve
  (# r: @real;
     setRadius: (# enter r #);
     area::< (# do r*r*3.145 #);
  #)

I find this hierarchy more 'correct', since neither can a circle
replace an ellipsis, nor the other way around.  At least not in the
semantic domain, you have laid out above.  

I hope this answers your question - otherwise try again.

Regards,

Jorgen Lindskov Knudsen

--
* Jorgen Lindskov Knudsen        | Phone:  +45 8942 3188             *
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