# encoding: utf-8

# Two ways of extending a class by class methods.
module M
  module ClassMethods
    def one
      'ok!'
    end

    def two
      'ok two!'
    end
  end
end

# I
class TestOne
  class << self
    include M::ClassMethods
  end
end

# II
class TestTwo
  extend M::ClassMethods
end

puts [
  TestOne.one, #=> ok!
  TestOne.two  #=> ok two!
]

puts [
  TestTwo.one, #=> ok!
  TestTwo.two  #=> ok two!
]

An example which illustrates the ways of extending a class by class methods.

Two ways of extending a class by class methods

class

Ruby