From: gwtmp01@...
Date: 2005-12-29T14:43:34+09:00
Subject: Re: Locking classes?


On Dec 29, 2005, at 12:04 AM, Steve Litt wrote:
> Yeah, on a similar subject, under what circumstances would one want  
> to add a
> method to an object if that method wasn't part of its class?

I'm going to use the term 'singleton method' to mean a method associated
with a single object.

Creating a singleton method on a class object is the idiom for creating
'class methods' in Ruby.  For example consider Date.today.  It doesn't
make sense to define the method 'today' in class 'Class' because we  
don't
want *all* classes to respond to 'today' but just one particular
class known as 'Date'.  So we make Date.today a singleton method on the
class object known as 'Date'.

Another common use of singleton methods is to override a method  
definition
for one particular object. In other languages this might be accomplished
by explicitly defining a subclass with the new method definition and  
then
creating an instance.  In Ruby, you create a regular instance of the  
base
class and then define a singleton method to override the definition from
the class.


Gary Wright