[RAILS] Getting Started with Ruby Modules

Getting Started with Ruby Modules

It is a module that is a function of Ruby, but I feel that it is one of the parts that is difficult to understand for those who are new to Ruby.

So this time I will summarize the modules.

Module function

● Mixins (include and extend) ● Creating namespaces ● Provide functions and methods

There are other features, but I've listed three main ones. Today I would like to take a look at these.


I don't know what it means to be a mixin, Multiple inheritance can be done by incorporating the module into the class. In Ruby, only single inheritance of class is possible, but module can be multiple inheritance. Also, unlike class, the same function can be shared even if it is not an is-a relationship (a relationship that an object is "an instance of a class or its descendant class").

Addendum: The explanation of the is-a relationship has been corrected. Thank you for your comment.



module Hoge
  def hello
    puts 'Hello'

module Bar
  def bye
    puts 'Bye'

class Greet
  #Include the module created above
  include Hoge
  include Bar

greet = Greet.new
greet.hello #=> "Hello"
greet.bye   #=> "Bye"

By including as above, the class can use the methods defined in the module. Adding a function by including a module in a class in this way is called a mixin.

extend You can use extend to turn a method in a module into a class method.


module Hoge
  def hello
    puts 'Hello'

class Greet
  #Extend the module created above
  extend Hoge

#You can call hello as a class method
Greet.hello #=> "Hello"

Like this, you can use the methods defined in the module with include or extend in the class. It is a mixin that is one of the ways to use the module.

Providing a namespace

If you write a class in the module name, it means a class that belongs to the module. You can prevent name conflicts.

module Bar
  class Baz
    def self.foo
      puts 'foo'

#I called the foo method from the Baz class that belongs to the module called Bar.
Bar::Baz.foo #=> "foo"

What I felt after working as an engineer There are many opportunities to use namespaces. Because the bigger the project, the more risky name conflicts will occur. We often set namespaces in this way to prevent collisions.

Define functions and methods


Constants defined in the module can be called via the module name.


module Hoge
  Year = "2020"

Hoge::Year #=> "2020"


Instance methods can be called by using the module_function method and making the method a module function.


module Hoge
  def hello
    puts 'Hello'

  module_function :hello

Hoge.hello #=> "Hello"

That concludes the module summary. Today was the 10th day of the serialization of an engineer who will become a full-fledged engineer 100 days later.

** 90 days to become a full-fledged engineer **

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