Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!husc6!psuvax1!burdvax!sdcrdcf!trwrb!felix!preston
From: preston@felix.UUCP (Preston Bannister)
Newsgroups: comp.lang.smalltalk
Subject: A question...
Message-ID: <4357@felix.UUCP>
Date: Mon, 3-Aug-87 20:24:33 EDT
Article-I.D.: felix.4357
Posted: Mon Aug  3 20:24:33 1987
Date-Received: Thu, 6-Aug-87 07:31:45 EDT
Sender: daemon@felix.UUCP
Reply-To: preston@felix.UUCP (Preston Bannister)
Organization: FileNet Corp., Costa Mesa, CA
Lines: 48


I have been writing a set of class definitions to support graphics in
Little Smalltalk from the descriptions in the Smalltalk-80 books.  

The class Point responds to '+'.  The examples show both:

	aPoint + aPoint		i.e.  (1 @ 2) + (3 @ 4) = (4 @ 6)

and

	aPoint + aNumber	i.e.  (1 @ 2) + 3 = (4 @ 5)

What I don't see is how to write the method for '+' without explicitly
testing the class of the parameter.  Something like:

  + delta
    (delta class == Point)
      ifTrue: [^ Point new x: (self x + (delta x)) y: (self y + (delta y)) ]
      ifFalse: [^ Point new x: (self x + delta) y: (self y + delta) ]

(This may not be correct Smalltalk.  I'm not that familiar with the
language and the book is not in front of me.)

Somehow I would have expected to write two methods:

  + aPoint
    ^ Point new x: (self x + (delta x)) y: (self y + (delta y)) 

  + aNumber
    ^ Point new x: (self x + delta) y: (self y + delta) 

But this doesn't seem possible.

Am I missing something??

========================================
Preston L. Bannister
USENET	   :	ucbvax!trwrb!felix!preston
BIX	   :	plb
CompuServe :	71350,3505
GEnie      :	p.bannister
--
========================================
Preston L. Bannister
USENET	   :	ucbvax!trwrb!felix!preston
BIX	   :	plb
CompuServe :	71350,3505
GEnie      :	p.bannister