クラスメソッド、得意メソッドの作り方

eigen.rb

# 得意メソッド、クラスメソッド定義２連発、３連発                                
# class << C, class << a, def self.foo, def a.foo
class C;end
  # (1)
class << C
  def foo
    puts 'OK'
  end
end
class C
  foo
end
class C
  # (2)
  def self.bar
    puts 'OK bar'
  end
end
C.bar
class C
  # (3)
  class << self
    def baz
      puts 'OK baz'
    end
  end
end
C.baz
# -------
a = "OK"
  # [1]
def a.foo
  puts 'OK foo'
end
a.foo
class << a
  # [2]
  def bar
    puts 'Or bar'
  end
end

a.bar