From: Steve Midgley <public@...>
Date: 2007-02-15T04:23:24+09:00
Subject: Creating a second instance of a singleton class?

Hey,

I've been working on a weird little problem that I thought people on 
this list might have a quick answer for (though the answer may be 
"impossible!"):

[code starts]

class Test; end

test = Test.new

class << test
   def new_method
     puts "new method is accessible!"
   end
end

test.new_method # works
test1 = test.dup # works but creates class from original class not 
singleton
test2 = class << test; self.new; end; # blows up with "can't create 
instance of virtual class (TypeError)"
# neither of these will therefore work
test1.new_method
test2.new_method

[code ends]

Basically, I have a class "Test" and I create an instance of it. I 
modify the instance's class definition (creating a singleton class 
definition).

Now what I really want is to create a second instance of the newly 
created singleton class. It appears to be impossible. A guess the name 
singleton implies as much. But with all of Ruby's tricks, I thought 
there'd be a way to create a new instance of a singleton.. Probably 
there is but I don't see it.

Hmm..

Steve

p.s. I've simplified the use-case way down - there are external reasons 
why I want to modify the singleton and create an instance of it, rather 
than modifying the parent class (or at least I think there are)..