Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!nosc!ucsd!ucsdhub!hp-sdd!hplabs!hpda!hpcuhb!hp-sde!hpcea!hpdtl!weeks
From: weeks@hpdtl.HP.COM (Gregory Weeks)
Newsgroups: comp.lang.smalltalk
Subject: implementing nonintrusive procedures
Message-ID: <7180001@hpdtl.HP.COM>
Date: 8 Sep 88 19:18:52 GMT
Organization: HP Design Tech. Lab., Palo Alto, CA
Lines: 23


I'm aware that the message-sending paradigm of Smalltalk doesn't smoothly
handle all situations.  There is one situation in particular that I'm
curious about.

Suppose I have a useful procedure in mind that accesses its argument only
by sending it certain messages.  Suppose further that I want to be able to
apply this procedure to any object that recognizes these messages.  There
are many ways to implement such a procedure.

1.  For every target class [that is, for every class that recognizes the
messages used in the procedure], define a method that implements the
procedure.

2.  Arrange somehow for all of the target classes to have a common
superclass and implement the procedure as a superclass method.

3.  Define a block that implements the procedure and bind it to a global
variable.

4.  Implement the procedure as a method of a nontarget class.

Are some of the above choices clearly superior?  Is there an established
Smalltalk style that rules out some of the choices?