From: ara.t.howard@...
Date: 2007-02-15T05:11:03+09:00
Subject: Re: Creating a second instance of a singleton class?

On Thu, 15 Feb 2007, Steve Midgley wrote:

> dblack wrote:
>
>> I think the idea is for the object to have its own class, so if that
>> class ceased to be its own class, there would have to be some new
>> construct that was its own class, and you'd be back where you started
>> :-)  So I don't think it's really possible in terms of the logic of
>> the model, and I can't think of any way to do it.
>> 
>> Is it possible you could use modules to bring about the kind of thing
>> you're looking for?
>
> Thanks David - I think I understand what you're saying.. I'd happily settle 
> for a *copy* of the instance's singleton class, but maybe I'm missing your 
> point?
>
> Another way to describe what I want to do:
>
> 1) create a class "Test"
> 2) create an instance of Test: "test1"
> 3) modify test1's class definition, creating a singleton class
> 4) Somehow "promote" or copy this singleton class to be a full fledged class 
> as "Test2"
> 5) Create an instance of "Test2" as "test2"

   harp:~ > cat a.rb
   require 'rubygems'
   require 'prototype'

   # 1)
   class Test; end

   # 2)
   test1 = Test.new

   # 3,4)
   Test2 = Class.new(test1.class){
     def new_method
       p 'no singleton class is needed'
     end
   }

   # 5)
   test2 = Test2.new

   test2.new_method


   harp:~ > ruby a.rb
   "no singleton class is needed"


> Obviously #4 is the place where I'm stuck. B/c I'm stuck, I am (as you 
> suggest) using module mix-in's to solve the problem, but it's less clean due 
> to my context in the code.. It'll work, but not as nicely as if there were a 
> method such as:
>
> Test2 = test1.dup_singleton_class
> test2 = Test2.new
>
> I can't see why Ruby would object inherently to copying all the class methods 
> of a singleton into a new class object (which is all I want - just a template 
> of the singleton class's methods - no class variables or whatnot).

you have to have the the class variables if you have class methods.  otherwise this

   class C
     @x = 42
     def self.x() @x end
   end

won't work

in strongly suspect there is an easier way to skin your cat.  can you tell us,
not what you are trying to do, but why?

-a
-- 
we can deny everything, except that we have the possibility of being better.
simply reflect on that.
- the dalai lama