What is a module?

A module is a collection of processes.

#Example: Caluculate module that summarizes addition and subtraction processing
module Calculate
  def add(a, b)
    a + b
  end

  def sub(a, b)
    a - b
  end
end

Difference between module and class

Modules and classes are similar, but with the following differences:

Module cannot be instantiated
Module cannot be inherited
Classes have processing and data, but modules have only processing

Module usage

The module is used for the following purposes.

Providing namespaces

The same class can be used as a different class by putting it in a module with a different name.

#Example: Include the same Image class in another module and different classes (User)::Image and Post::Treat as Image)
module User
  class Image
    def self.hoge
      puts 'user image'
    end
  end
end

module Post
  class Image
    def self.hoge
      puts 'post image'
    end
  end
end

User::Image.hoge #=> "user image"
Post::Image.hoge #=> "post image"

Incorporate into a class as an instance method

You can use the include method to include the module processing as an instance method of the target class.

#Example: Incorporate User module as an instance method of Image class

module User
  def hoge
    puts 'user image'
  end
end

class Image
  include User
end

image = Image.new
image.hoge #=> "user image"

Incorporate into a class as a class method

You can use the extend method to import the module processing as a class method of the target class.

#Example: Incorporate User module as class method of Image class

module User
  def hoge
    puts 'user image'
  end
end

class Image
  extend User
end

Image.hoge #=> "user image"

Summary

Module is a collection of processes
Modules, unlike classes, cannot be instantiated or inherited
Can provide namespaces and can be incorporated into classes as instance methods / class methods

What is a Ruby module?