metaid.rb

# Author : why the lucky stiff 
# include in any project in which metaprogramming is needed 

class Object
   # The hidden singleton lurks behind everyone
   def metaclass; class << self; self; end; end

   # The equivalent of class_eval for singleton classes.
   # Evaluates the given block in
   # the context of the receiver’s singleton class.
   def meta_eval &blk; metaclass.instance_eval &blk; end

   # Adds methods to a metaclass
   # Defines a method within the receiver’s singleton class. 
   # If the receiver is a class or module, this will create 
   # a class method (instance method of the receiver’s singleton
   # class).
   def meta_def name, &blk
     meta_eval { define_method name, &blk }
   end

   # Defines an instance method within a class
   # Defines an instance method in the receiver 
   # (which must be a class or module).
   def class_def name, &blk
     class_eval { define_method name, &blk }
   end
 end