From: dblack@...
Date: 2006-02-17T01:56:00+09:00
Subject: Re: Newbie: how to dynamically add methods?

Hi --

On Fri, 17 Feb 2006, Jeff Cohen wrote:

> The PickAxe doesn't seem to cover details of how to dynamically create
> class or add methods to existing classes.  For example, sometimes I see
> people doing things like this:
>
> class << self
>  ...
>
> and I'm wondering exactly what's going on.

The "<< obj" notation takes you into the singleton class of obj, which
is where that particular object's singleton methods (i.e., those that
only that object can call) are stored.

Except for some minor differences that usually don't matter, these two
things are equivalent:

   def a.meth
   end

and

   class << a
     def meth
     end
   end

In both cases, you're defining a method that only the object a can
call.

> Anybody know of a good book or online tutorial for this kind of thing?

http://www.rubygarden.org/ruby?SingletonTutorial goes over singleton
classes and methods, and also the other meaning of "singleton" in
Ruby (not closely related, except by coincidence of name, but good to
know about *because* of the coincidence of name).


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black