From: Christoph <chr_mail@...>
Date: 2005-05-01T09:34:08+09:00
Subject: Re: instantiating metaclasses, sorta [Was: determining when inside 'class << self']

Jim Freeze schrieb:

>* Mark Hubbart <discordantus@gmail.com> [2005-04-30 16:35:16 +0900]:
>
>  
>
>>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.
>>    
>>
>
>As is said later, duping the object 'erases' the singleton methods
>while 'cloning' carries them over.
>
>I've always considered duping as a nice way of erasing the 'specialness'
>of an object while returning it to its natural state.
>  
>
It's true that duping erases class method for general
objects - it's  FALSE for  Module objects!

---
module A
    def self.bla
      puts "bla"
    end
end

A.dup.bla # bla


Foo = class << 1.0; def self.bar; puts "bar" end; self end.dup

class Bar < Foo
    puts ancestors.join(" < ")
     # Bar < Foo < Float < Precision < Numeric < Comparable < Object < 
Kernel
end

Bar.bar # bar
---

I am not sure if I would read to much into this behavior.
Here is another curiosity. If you clone a singleton you end up
with a "virtual class" which is not the virtual class of any living
Object. I guess the only usefully thing you can do with this class
is duping it:-)

---
Once  = class << one = []; self end
Twice = Once.clone

begin
 Class.new(Twice)
rescue TypeError=> mes
 puts mes  # can't make subclass of virtual class
end

class Once
    def okay
    end
end

class Twice
    def fails
    end
end

one.okay

begin
  one.fails
rescue NoMethodError=> mes
 puts mes  # undefined method `fails' for []:Array
end

found = nil
ObjectSpace.each_object do |o|
    found =  o if Twice == class << o; self end
end

p found # nil

class Third <  Twice.dup
end

p Third.new(1){3} # [3]

---
/Christoph