Extend for class methods in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of extending a module for class methods

What is the output of this Ruby code when the class method greet is called?

Ruby

module Friendly
  def greet
    "Hello from module"
  end
end

class Person
  extend Friendly
end

puts Person.greet

A "Hello from module"

B SyntaxError: unexpected keyword_end

C NoMethodError: undefined method `greet' for Person:Class

D "Hello from instance"

💡 Hint

Remember that extend adds module methods as class methods.

Using extend Friendly inside the class adds the module's methods as class methods. So Person.greet calls the module's greet method and returns "Hello from module".

❓ Predict Output

intermediate

Effect of including vs extending a module

What will be the output of this Ruby code?

Ruby

module Talk
  def speak
    "Speaking"
  end
end

class Animal
  include Talk
end

class Robot
  extend Talk
end

puts Animal.new.speak
puts Robot.speak

A

NoMethodError: undefined method `speak' for Animal:Class
Speaking

B NoMethodError for both calls

C

Speaking
Speaking

D

Speaking
NoMethodError: undefined method `speak' for Robot:Class

💡 Hint

Including adds instance methods; extending adds class methods.

Including Talk adds speak as an instance method to Animal. Extending Talk adds speak as a class method to Robot. Both calls print "Speaking".

🔧 Debug

advanced

Why does this class method call fail?

Given this Ruby code, why does calling Car.honk raise an error?

Ruby

module Sounds
  def honk
    "Beep beep!"
  end
end

class Car
  include Sounds
end

puts Car.honk

A Because the module method <code>honk</code> is private and cannot be called.

B Because <code>include</code> adds instance methods, not class methods, so <code>Car.honk</code> is undefined.

C Because <code>Car</code> forgot to inherit from <code>Sounds</code>.

D Because <code>honk</code> is defined with wrong syntax inside the module.

💡 Hint

Think about the difference between include and extend.

Using include Sounds adds honk as an instance method to Car. Calling Car.honk tries to call a class method, which does not exist, causing a NoMethodError.

📝 Syntax

advanced

Identify the syntax error in extending a module

Which option contains a syntax error when trying to add class methods using a module?

Ruby

module Greetings
  def hello
    "Hi!"
  end
end

class User
  extend Greetings
end

A

class User
  extend Greetings.new
end

B

class User
  extend(Greetings)
end

C

class User
  extend Greetings()
end

D

class User
  extend Greetings
end

💡 Hint

Remember how to use extend with modules.

Modules cannot be instantiated with .new. Option A tries to call Greetings.new, which causes a NoMethodError. The other options correctly extend the module as class methods.

🚀 Application

expert

How to add both instance and class methods from a module

You want to add instance methods and class methods from a single module Features to a class Gadget. Which code correctly achieves this?

Ruby

module Features
  def instance_feature
    "Instance method"
  end

  module ClassMethods
    def class_feature
      "Class method"
    end
  end
end

class Gadget
  # What goes here?
end

puts Gadget.new.instance_feature
puts Gadget.class_feature

A

class Gadget
  extend Features
  extend Features::ClassMethods
end

B

class Gadget
  extend Features
  include Features::ClassMethods
end

C

class Gadget
  include Features
  include Features::ClassMethods
end

D

class Gadget
  include Features
  extend Features::ClassMethods
end

💡 Hint

Use include for instance methods and extend for class methods.

Including Features adds instance_feature as an instance method. Extending Features::ClassMethods adds class_feature as a class method. This pattern cleanly separates instance and class methods.