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Modules in Ruby

Introduction to Modules in Ruby

Modules in Ruby serve a fundamental role in organizing code. They resemble classes but cannot be instantiated.

As the core essence of Ruby’s programming design, developers use them to bundle logically related objects together, helping maintain order and understandability in complex projects.

Understanding Ruby Modules

Defining a Module

Think of Ruby modules as a toolbox: they hold a collection of methods, constants, and variables, all packed together for convenient use. They are defined much like a class, using the keyword module, followed by the module name.

Include, Prepend, and Extend Keywords

These keywords enable the mixing of a module into a class or another module. The keyword include permits classes to use methods from the module as instance methods. The keyword extend allows the inclusion of module methods as class methods.

The Importance of Namespacing

Namespacing is a powerful feature of Ruby modules. It is a way of bundling related objects together, hence promoting clean, organized code.

Modules and Inheritance

Ruby does not handle multiple inheritances. However, it facilitates the use of composition via the mixin facility. We can include a module in another module or a class, which avails the included module’s method in the host module or class. You can find more information about modules and inheritance here.

Working with Ruby Modules

Creation of a Module

Creating a module in Ruby is a straightforward process. We begin by using the module keyword, followed by the module’s name. We can define methods, instance variables, and constants inside the module.

Including a Module

Including a module in a class is done using the keyword include. This makes the methods defined in the module available as instance methods in the class.

Using Mixins

Mixins are a powerful way to add functionality to classes. When a class encounters a missing method, Ruby searches within the mixins for the method; if located, it is utilized. This approach serves as a substitute for multiple inheritances, a concept not supported by Ruby.

Understanding Ancestor Chains with Modules

The keyword include inserts the module in the ancestor chain right after the class, while the keyword extend places the module in the singleton class’s ancestor chain. Understanding this is crucial while dealing with inherited methods in Ruby.


Ruby modules are paramount for efficient and organized code. They allow for the neat encapsulation of related methods, constants, and variables, essentially keeping your code DRY (Don’t Repeat Yourself).

Whether for implementing mixin functionalities in place of multiple inheritances or namespacing to logically bundle objects together, understanding and effectively using modules is an indispensable part of Ruby programming.

Continue with this tutorial series to gain more understanding of Ruby programming. The previous article Introduction to Classes and Objects in Ruby discussed the fundamentals of classes in Ruby. Next article to come: Stay with us on this learning journey!


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