module

http://lizabinante.com/blog/modules-and-self-in-ruby/

Module Mixin

extend vs. include in classes

• include: instance methods

• extend: class methods

module Animals
  def mammals
    ["sloths", "puppies", "porcupines"]
  end
end

# - - - - - - - - include
class Zoo
  include Animals
end

zoo = Zoo.new
zoo.mammals # => ["sloths", "puppies", "porcupines"]
zoo.methods - Object.methods # => mammals

# - - - - - - - - extend
class PetStore
  extend Animals
end

PetStore.mammals # => ["sloths", "puppies", "porcupines"]
pet_store = PetStore.new
pet_store.mammals # => undefined method `mammals' for #<PetStore:0x007f858a919f30> (NoMethodError)

PetStore.methods - Object.methods # => mammals
pet_store = PetStore.new
pet_store.methods - Object.methods # =>

Module Methods

extend self:

• Not change the behavior of include or extend in your classes

self method name prefix

• change the behavior of include or extend in your classes (self prefix can not be mixed in)

• only access some of methods in module (access self prefix only)

extend self

module Animals
  extend self

  def mammals
    ["sloths", "puppies", "porcupines"]
  end

  def sea_creatures
    ["narwhal", "starfish", "dolphin"]
  end
end

Animals.mammals # => ["sloths", "puppies", "porcupines"]
Animals.sea_creatures # => ["narwhal", "starfish", "dolphin"]

# - - - - - - - - include
class Zoo
  include Animals
end

Zoo.mammals # => undefined method `mammals' for Zoo:Class (NoMethodError)
zoo = Zoo.new
zoo.mammals # => ["sloths", "puppies", "porcupines"]

# - - - - - - - - extend
class PetStore
  extend Animals
end

PetStore.mammals # => ["sloths", "puppies", "porcupines"]
pet_store = PetStore.new
pet_store.mammals # => undefined method `mammals' for #<PetStore:0x007f858a919f30> (NoMethodError)

self method name prefix

module Animals
  def self.mammals
    ["sloths", "puppies", "porcupines"]
  end

  def sea_creatures
    ["narwhal", "starfish", "dolphin"]
  end
end

Animals.mammals # => ["sloths", "puppies", "porcupines"]
Animals.sea_creatures # => undefined method

# - - - - - - - - include
class Zoo
  include Animals
end

Zoo.mammals # => undefined method
Zoo.sea_creatures # => undefined method
zoo = Zoo.new
zoo.mammals # => undefined method
zoo.sea_creatures # => ["narwhal", "starfish", "dolphin"]

# - - - - - - - - extend
class PetStore
  extend Animals
end

PetStore.mammals # => undefined method
PetStore.sea_creatures # => ["narwhal", "starfish", "dolphin"]

pet_store = PetStore.new
pet_store.mammals # => undefined method
pet_store.sea_creatures # => undefined method