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From: chips@usfvax2.UUCP (Chip Salzenberg)
Newsgroups: comp.lang.smalltalk
Subject: Re: A question...
Message-ID: <814@usfvax2.UUCP>
Date: Thu, 6-Aug-87 10:15:26 EDT
Article-I.D.: usfvax2.814
Posted: Thu Aug  6 10:15:26 1987
Date-Received: Sat, 8-Aug-87 11:05:27 EDT
References: <4357@felix.UUCP>
Organization: AT Engineering, Tampa, FL
Lines: 41
Summary: How about "asPoint"?

In article <4357@felix.UUCP>, preston@felix.UUCP writes:
> 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.
> 
> Preston L. Bannister
> USENET	   :	ucbvax!trwrb!felix!preston

Perhaps you could implement the method asPoint in the class Integer:

	asPoint
	"Return a Point with x and y both equal to self."
	^self @ self.

Then, in class Point:

	asPoint
	"Return self."
	^self.

and, then the method you wanted:

	+ delta
	"Return the sum of two points.  Delta may be an integer."
	| aPoint |
	aPoint := delta asPoint.
	^(self x) + (aPoint x) @ (self y) + (aPoint y).

This may not be very fast, but it would work.
-- 
Chip Salzenberg            UUCP: "uunet!ateng!chip"  or  "chips@usfvax2.UUCP"
A.T. Engineering, Tampa    Fidonet: 137/42    CIS: 73717,366
"Use the Source, Luke!"    My opinions do not necessarily agree with anything.