Module methods in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of calling a module method directly

What is the output of this Ruby code?

Ruby

module Greetings
  def self.say_hello
    "Hello from module!"
  end
end

puts Greetings.say_hello

A Hello from module!

B NoMethodError

C nil

D SyntaxError

💡 Hint

Look at how the method is defined with self. It means it belongs to the module itself.

The method say_hello is defined as a module method using self. It can be called directly on the module name. So it prints the string.

❓ Predict Output

intermediate

Output of including a module with a module method

What happens when you include a module with a module method and call that method on the including class?

Ruby

module Tools
  def self.info
    "Tools module info"
  end
end

class Machine
  include Tools
end

puts Machine.info

A Tools module info

B NoMethodError

C nil

D SyntaxError

💡 Hint

Including a module adds instance methods, but module methods are not included as class methods.

Including a module adds its instance methods to the class. But module methods defined with self are not included. So Machine.info is undefined and raises NoMethodError.

🔧 Debug

advanced

Fix the code to call a module method from a class

This code tries to call a module method from a class method but raises an error. Which option fixes it?

Ruby

module MathHelpers
  def self.square(x)
    x * x
  end
end

class Calculator
  def self.square(x)
    square(x)
  end
end

puts Calculator.square(4)

A Change MathHelpers.square to def square(x) without self

B Add include MathHelpers inside Calculator

C Change Calculator.square to call MathHelpers.square(x)

D Change Calculator.square to an instance method

💡 Hint

Module methods with self need to be called with the module name.

The Calculator class method tries to call square(x) but no such method exists in Calculator. Calling MathHelpers.square(x) fixes the error.

📝 Syntax

advanced

Identify the syntax error in module method definition

Which option shows the correct way to define a module method in Ruby?

A

module M
  def method:
    puts 'Hi'
  end
end

B

module M
  def method(self)
    puts 'Hi'
  end
end

C

module M
  def method.self
    puts 'Hi'
  end
end

D

module M
  def self.method
    puts 'Hi'
  end
end

💡 Hint

Module methods use self. before the method name.

Option D correctly defines a module method using def self.method. Other options have invalid syntax.

🚀 Application

expert

How many methods does this module add to a class?

Given this module and class, how many methods does the class have after including the module?

Ruby

module Features
  def self.module_method
    'module method'
  end

  def instance_method
    'instance method'
  end
end

class Product
  include Features
end

methods = Product.methods - Object.methods
instance_methods = Product.instance_methods(false)

A methods: 0, instance_methods: 1

B methods: 1, instance_methods: 1

C methods: 1, instance_methods: 0

D methods: 0, instance_methods: 0

💡 Hint

Including a module adds instance methods, but not module methods as class methods.

The module method defined with self is not added to the class methods. The instance_method is added as an instance method. So Product.methods - Object.methods is empty (0), and Product.instance_methods(false) includes :instance_method (1).