From: Mark Hubbart <discordantus@...>
Date: 2005-05-01T05:31:02+09:00
Subject: Re: instantiating metaclasses, sorta [Was: determining when inside 'class << self']

On 4/30/05, David A. Black <dblack@wobblini.net> wrote:
> 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....

Sure enough, this doesn't work in 1.6.8. Also, the singleton class
inspects as "String" in 1.6.8, which I find interesting.

> 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... :-)

indeed :)

cheers,
Mark