Ruby: meta-programming

gistfile1.rb

    #definition
    class Object < BasicObject
      include Kernel
      ...
    end

    #examples
    module M; end
    class C; include M; end
    C.ancestors  # => [M, Object, Kernel, BasicObject]
    
    #eigenclass, metaclass or sington class is a hidden class for each object,
    #which only have one instance, where sington methods lives.
    #use following to define singleton class.
    class << self; self; end

    #1. superclass of metaclass of object is object's class
    #2. superclass of metaclass of class  is metaclass of class's superclass