Path: news.daimi.aau.dk!news.daimi.aau.dk!miksen
From: miksen@peseta.daimi.aau.dk (Michael Thomsen)
Newsgroups: comp.lang.beta
Subject: Re: polymorphism
Date: 30 Dec 1995 17:10:06 GMT
Organization: DAIMI, Computer Science Dept. of Aarhus Univ.
Lines: 76
Message-ID: <MIKSEN.95Dec30181006@peseta.daimi.aau.dk>
References: <4bnjm4$cvg@krone.daimi.aau.dk> <4bp52o$kp4@netnews.upenn.edu>
NNTP-Posting-Host: peseta.daimi.aau.dk
In-reply-to: Wolfgang Ziller's message of 26 Dec 1995 15:41:12 GMT

In article <4bp52o$kp4@netnews.upenn.edu> Wolfgang Ziller <wziller@math.upenn.edu> writes:
#
#   Albertina Lourenci <AL@BRUSPSCE.BitNet> wrote:
#   >Hi, all|
#   >        Could someone tell me if BETA supports polymorphism? If yes,
#   >can you demonstrate how? Special thanks.
#
#   Yes, polymorphism is a vital part of Object-Oriented 
#   Technology.  BETA does support it and I believe the 
#   following code is correct:
#
#   polygon: (# draw:< (# do inner #) #);
#   circle: (# draw:<< (# do (* draw a circle *) #);
#   square: (# draw:<< (# do (* draw a sqare *) #);
#
#  (#
#       a_polygon: @polygon;
#       a_circle: @circle;
#       a_square: @sqaure;
#   do
#       a_circle -> a_polygon;
#       a_polygon.draw;
#       a_square -> a_polygon;
#       a_polygon.draw;
#   #);
#

Well it should probably be a bit more like:

(#
   polygon: (# draw:< (# do 'polygon ' -> puttext; inner #) #);
   circle: polygon(# draw::< (# do 'circle' -> putline; (* draw a circle *) #); #);
   square: polygon(# draw::< (# do 'square' -> putline; (* draw a sqare *) #); #);

   a_polygon: ^polygon;
   a_circle: @circle;
   a_square: @square;
do
   a_circle[] -> a_polygon[];
   a_polygon.draw;
   a_square[] -> a_polygon[];
   a_polygon.draw;
#)

Which would print:

    polygon circle
    polygon square
 

#   That's roughly the idea.  I'm not sure if the above code is 
#   totally correct (esp. the a_polygon.draw parts.  Also not
#   sure if you could condense the above and write 
#   a_circle -> a_polygon.draw).  Anyway, BETA definately
#   supports polymorphism.


If you mean: a_circle[] -> a_poly.draw[] , then the answer is no. This 
would mean: assign the reference to a_circle to the enter part of 
a_poly.draw. Clearly a_poly.draw hasn't got an enter part. 

#
#   Regards,
#   Wolfgang Ziller


Kind Regards, Michael Thomsen...




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