From: Carlos <angus@...>
Date: 2004-03-09T02:13:59+09:00
Subject: Re: proposal:  class<<obj to invoke extend_object

["David A. Black" <dblack@wobblini.net>, 2004-03-08 17.53 CET]
> Here's a brute-force but perhaps useable implementation:
> 
>   class Class
>     def single_instance
>       ObjectSpace.each_object do |obj|
> 	c = (class << obj; self; end)
> 	return obj if c == self
>       end
>     end
>   end
> 
>   p (class << "hello"; self; end).single_instance   # "hello"

In fact, there seems to be an instance variable named "__attached__"
in singleton classes, that is linked to the instance. It is not
accessible from ruby (because it doesn't start with "@"); I guess this
is a design decision (?).