Ruby Academy · Lesson

Defining Modules

Namespaces and methods.

Lesson 1 of 413 steps

Defining Modules is a free Ruby Academy lesson on CoddyKit. This is lesson 1 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Ruby Academy learning path, and your progress syncs across the web and the CoddyKit app. The Ruby Academy course includes 4 lessons in total.

Namespaces and Methods

A module is a container for methods and constants. Unlike a class, you cannot create an instance of a module. Modules serve two roles: grouping code (namespacing) and sharing behavior (mixins).

module Greeter
  def self.hello
    "Hello from the module"
  end
end
puts Greeter.hello

Module Methods

Define a method with self. to call it directly on the module, like a utility function. These are often called module functions.

module MathTools
  def self.square(x)
    x * x
  end
end
puts MathTools.square(7)

Module Constants

Modules hold constants too. Access them with the scope operator ::.

module Physics
  GRAVITY = 9.81
end
puts Physics::GRAVITY

Namespacing Classes

Wrap classes in a module to avoid name collisions. The full name uses ::.

module Store
  class Item
    def initialize(name)
      @name = name
    end
    def to_s
      @name
    end
  end
end
puts Store::Item.new("Book")

Why Namespaces Matter

Two libraries might both define a Logger. Namespacing keeps them apart: Audio::Logger and Network::Logger never clash.

module Audio
  class Logger
    def name; "audio logger"; end
  end
end
module Network
  class Logger
    def name; "network logger"; end
  end
end
puts Audio::Logger.new.name
puts Network::Logger.new.name

module_function

module_function makes the following methods callable both on the module and as private instance methods when mixed in. It avoids repeating self..

module Calc
  module_function
  def add(a, b)
    a + b
  end
end
puts Calc.add(2, 3)

Grouping Related Constants

Modules are great for organizing related configuration values under one clear name.

module Color
  RED = "#FF0000"
  GREEN = "#00FF00"
  BLUE = "#0000FF"
end
puts Color::GREEN

Nested Modules

Modules can nest inside other modules for deeper organization.

module App
  module Config
    VERSION = "1.0"
  end
end
puts App::Config::VERSION

Listing Module Contents

Reflection methods let you inspect a module's constants and methods at runtime.

module Settings
  WIDTH = 80
  HEIGHT = 24
end
p Settings.constants

Modules Cannot Be Instantiated

Trying Module.new on a named module style fails because a module has no constructor for instances. It is a namespace and behavior holder, not a blueprint for objects.

module Tools
end
begin
  Tools.new
rescue NoMethodError => e
  puts "Cannot instantiate: #{e.message}"
end

Putting It Together

Modules organize and share code:

Use self.method for callable module functions.
Hold constants accessed with ::.
Namespace classes to prevent collisions.
You cannot instantiate a module.

module Geometry
  PI = 3.14159
  def self.circle_area(r)
    PI * r * r
  end
end
puts Geometry.circle_area(2)

Quick Check

Test your understanding of modules.

Answer it in the interactive lesson

Recap

You learned to define modules:

Modules group methods and constants.
self.method defines callable module functions.
:: accesses constants and nested classes.
Namespacing prevents naming clashes.

module Util
  def self.shout(s)
    s.upcase + "!"
  end
end
puts Util.shout("ruby")

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Frequently Asked Questions

Is the “Defining Modules” lesson free?

Yes — any 3 lessons of the Ruby Academy learning path, including “Defining Modules”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Ruby Academy course includes 4 lessons in total.

What will I learn in “Defining Modules”?

Namespaces and methods. You practise Ruby Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Ruby Academy?

No prior experience is required. Ruby Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 4.

How long does the “Defining Modules” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Ruby Academy lesson?

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