include と extend

振る舞いのミックスイン

module Walkable
  def walk
    "#{name} is walking"
  end
end
class Person
  include Walkable
  attr_reader :name
  def initialize(name)
    @name = name
  end
end
puts Person.new("Ada").walk

includeでインスタンスメソッドを追加する

module Sayable
  def say(msg)
    "#{msg}!"
  end
end
class Dog
  include Sayable
end
puts Dog.new.say("Woof")

クラス間で再利用する

module Timestamped
  def stamp
    "created"
  end
end
class Post; include Timestamped; end
class Comment; include Timestamped; end
puts Post.new.stamp
puts Comment.new.stamp

extendでクラスメソッドを追加する

module Findable
  def find(id)
    "Finding record #{id}"
  end
end
class User
  extend Findable
end
puts User.find(42)

オブジェクトに対するextend

module Admin
  def privileges
    "all access"
  end
end
user = Object.new
user.extend(Admin)
puts user.privileges

includeとextendの違い

module Helper
  def help; "helping"; end
end
class A; include Helper; end
class B; extend Helper; end
puts A.new.help
puts B.help

モジュールからホストのメソッドを利用できる

module Describable
  def describe
    "I am #{role}"
  end
end
class Worker
  include Describable
  def role; "a worker"; end
end
puts Worker.new.describe

includedフック

module Trackable
  def self.included(base)
    puts "Trackable added to #{base}"
  end
end
class Order
  include Trackable
end

所属を確認する

module Flyable; end
class Bird; include Flyable; end
b = Bird.new
puts b.is_a?(Flyable)
p Bird.ancestors

複数のミックスインを組み合わせる

module Swimmable; def swim; "swimming"; end; end
module Runnable; def run; "running"; end; end
class Athlete
  include Swimmable
  include Runnable
end
a = Athlete.new
puts a.swim
puts a.run

まとめ

module Greet
  def hi; "hi from #{self.class}"; end
end
class Cat; include Greet; end
puts Cat.new.hi

理解度チェック

振り返り

module Loud
  def shout(s); s.upcase; end
end
class Speaker; include Loud; end
puts Speaker.new.shout("hello")