lab rat

lab_rat.rb

# see Metaprogramming Ruby, p. 108
class C
  def a_method
    "C#a_method"
  end

  def eigenclass
    class << self; self; end
  end
end

class D < C;
  def self.a_class_method
    'D.a_class_method'
  end
end

obj = D.new

class << obj
  def a_singleton_method
    'obj#a_singleton_method'
  end
end

class C
  class << self
    def a_class_method
      'C.a_class_method'
    end

    def eigenclass
      class << self
        self
      end
    end
  end
end

puts "*** no eigenclass ***"
puts obj.class                            # D
puts obj.class.superclass                 # C
puts obj.a_method                         # C#a_method
puts obj.a_singleton_method               # obj#a_singleton_method
puts obj.class.a_class_method             # D.a_class_method
puts C.a_class_method                     # C.a_class_method
puts obj.class.superclass.a_class_method  # C.a_class_method

puts "*** with eigenclass ***"
puts obj.eigenclass                 # #<Class:#D>
puts obj.eigenclass.a_class_method  # D.a_class_method
puts obj.eigenclass.superclass      # #<Class:D>
puts C.eigenclass                   # #<Class:C>
puts C.eigenclass.superclass        # #<Class:Class>