From: "David A. Black" <dblack@...>
Date: 2005-05-01T00:23:47+09:00
Subject: Re: instantiating metaclasses, sorta [Was: determining when inside 'class << self']

Hi --

On Sat, 30 Apr 2005, Mark Hubbart wrote:

> While experimenting with this, I discovered something interesting: it
> is possible to instantiate a metaclass. By duping a metaclass, you
> regain the ability to instantiate it, apparently without losing any
> functionality.
>
>  name = "Jack Smith"
>  def name.reverse
>    split.reverse.join ", "
>  end
>  name.reverse  #==> "Smith, Jack"
>
>  # dup name's metaclass
>  nameclass = class << name; self; end.dup
>
>  name2 = nameclass.new  "John Doe"
>  name2.reverse  #==> "Doe, John"
>
> Any thoughts? Am I strange for finding this a bit surprising?

I find it pretty startling.  I've often wondered whether there was a
way to do essentially this.  I'd concluded there wasn't.  Maybe, at
the time, there wasn't....

I subjected it to one further test, to make sure that the
name2.reverse is actually a different method (since if two objects
were sharing a singleton method, that would have to be considered a
bug):

   class << name
     def reverse
       "hi"
     end
   end

   name.reverse         # hi
   name2.reverse        # Doe, John
   "hello".reverse      # olleh      <= just to be totally sure :-)

Hmmmm, it's still daytime in Paris, so we may yet learn of some
limitation or reason to avoid it... :-)


David

-- 
David A. Black
dblack@wobblini.net