From: ara.t.howard@...
Date: 2007-02-15T05:25:11+09:00
Subject: Re: Creating a second instance of a singleton class?

On Thu, 15 Feb 2007 Ara.T.Howard@noaa.gov wrote:

> 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"

and, if it is

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

   # 1)
   class Test; end

   # 2)
   test1 = Test.new

   # 3)
   m = Module.new{
     def new_method
       p 'if a singleton class is needed'
     end
   }
   (class << test1; self; end).module_eval{ include m }

   # much easier - no singleton class needed here either
   # test1.extend m

   # 4)
   Test2 = Class.new(test1.class){ include m }

   # 5)
   test2 = Test2.new

   test2.new_method


   harp:~ > ruby a.rb
   "if a singleton class is needed"


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