Hacking Object.new to ensure that only one instance of an object exists in memory

singleton_foo.rb

# Don't use this in a real project never!!!
class SingletonFoo < Object
  def self.new(*args)
    first_instance = ObjectSpace.each_object(self).first
    return first_instance if first_instance
    object = allocate
    object.send(:initialize, *args)
    object
  end
end

singleton_foo_irb.txt

ruby-1.9.2-p290 :057 > SingletonFoo.new
 => #<SingletonFoo:0x00000102077170> 

ruby-1.9.2-p290 :058 > SingletonFoo.new
 => #<SingletonFoo:0x00000102077170> 

ruby-1.9.2-p290 :059 > SingletonFoo.new
 => #<SingletonFoo:0x00000102077170> 

ruby-1.9.2-p290 :060 > SingletonFoo.new
 => #<SingletonFoo:0x00000102077170> 

ruby-1.9.2-p290 :061 > SingletonFoo.new
 => #<SingletonFoo:0x00000102077170>

ruby-1.9.2-p290 :062 > SingletonFoo.new == SingletonFoo.new
 => true 

ruby-1.9.2-p290 :063 > SingletonFoo.new.object_id == SingletonFoo.new.object_id
 => true