How to Include Module in Ruby: Syntax and Examples

In Ruby, you include a module into a class using the include keyword followed by the module name. This adds the module's methods as instance methods to the class, allowing you to reuse code easily.

Syntax

Use the include keyword inside a class to add a module's methods as instance methods. The module name follows include.

• include: keyword to add module methods
• ModuleName: the module you want to include

ruby

module Greetings
  def hello
    "Hello!"
  end
end

class Person
  include Greetings
end

Example

This example shows a module Greetings with a method hello. The class Person includes this module, so its instances can call hello.

ruby

module Greetings
  def hello
    "Hello!"
  end
end

class Person
  include Greetings
end

person = Person.new
puts person.hello

Output

Hello!

Common Pitfalls

One common mistake is trying to call module methods directly on the class without including the module. Another is confusing include with extend, which adds methods as class methods instead of instance methods.

ruby

module Greetings
  def hello
    "Hello!"
  end
end

class Person
  # Wrong: calling module method without include
  # puts hello # Error: undefined method

  # Correct: include module to use instance methods
  include Greetings
end

person = Person.new
puts person.hello

Output

Hello!

Quick Reference

Keyword	Purpose
include ModuleName	Adds module methods as instance methods to a class
extend ModuleName	Adds module methods as class methods to a class
ModuleName.method_name	Call module method directly if defined as module method

Key Takeaways

Use include ModuleName inside a class to add module methods as instance methods.

Including a module allows code reuse by sharing methods across classes.

Do not confuse include (instance methods) with extend (class methods).

You must include the module before calling its methods on class instances.

Modules help organize and share behavior without inheritance.