Custom modules as mixins in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a class using a module mixin

What is the output of this Ruby code when the Dog object calls sound?

Ruby

module AnimalSounds
  def sound
    "Generic sound"
  end
end

class Dog
  include AnimalSounds
  def sound
    "Bark"
  end
end

puts Dog.new.sound

A "Bark"

B RuntimeError

C "Generic sound"

D nil

💡 Hint

Remember that methods defined in the class override those from included modules.

The Dog class includes the AnimalSounds module, but it also defines its own sound method. The class method overrides the module method, so calling sound on a Dog instance returns "Bark".

🧠 Conceptual

intermediate

Purpose of using modules as mixins

Why do Ruby programmers use modules as mixins instead of inheritance?

A To create instances of modules directly

B To share reusable code across unrelated classes without using inheritance

C To replace classes entirely

D To prevent any method overriding

💡 Hint

Think about code reuse and class relationships.

Modules as mixins allow sharing methods across different classes that do not share a parent-child relationship. This avoids the limitations of single inheritance and promotes code reuse.

🔧 Debug

advanced

Identify the error in module mixin usage

What error will this Ruby code produce?

Ruby

module Greetings
  def greet
    "Hello!"
  end
end

class Person
  extend Greetings
end

puts Person.new.greet

A SyntaxError

B TypeError

C NoMethodError: undefined method 'greet' for #<Person:...>

D Prints "Hello!"

💡 Hint

Check how extend and include differ in Ruby.

Using extend Greetings adds the module methods as class methods, not instance methods. Since greet is called on an instance, it raises a NoMethodError.

📝 Syntax

advanced

Correct syntax to include a module as a mixin

Which option correctly includes the Flyable module as a mixin in the Bird class?

Ruby

module Flyable
  def fly
    "I can fly!"
  end
end

class Bird
  # Which line correctly mixes in Flyable?
end

A include Flyable

B extend Flyable

C import Flyable

D use Flyable

💡 Hint

Remember the keyword to add instance methods from a module.

The include keyword mixes in module methods as instance methods. extend adds them as class methods. import and use are not Ruby keywords.

🚀 Application

expert

Predict the output with multiple mixins and method lookup

What will this Ruby code print?

Ruby

module A
  def message
    "From A"
  end
end

module B
  def message
    "From B"
  end
end

class C
  include A
  include B
end

puts C.new.message

A "From A"

B RuntimeError

C nil

D "From B"

💡 Hint

In Ruby, the last included module's methods override earlier ones.

When multiple modules are included, Ruby uses the method from the last included module. Here, B is included after A, so message from B is called.