Include for instance methods in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using include?

Consider the following Ruby code that uses include to add instance methods from a module to a class. What will be printed when the code runs?

Ruby

module Greetings
  def hello
    "Hello from module!"
  end
end

class Person
  include Greetings
end

p = Person.new
puts p.hello

A SyntaxError: unexpected keyword_end

B Hello from module!

C nil

D NoMethodError: undefined method `hello' for #<Person:0x000...>

💡 Hint

Remember that include adds module methods as instance methods to the class.

The include Greetings line adds the hello method from the Greetings module as an instance method to the Person class. So calling p.hello prints "Hello from module!".

❓ Predict Output

intermediate

What happens if you call a module method without including it?

Look at this Ruby code where a module method is called on an instance of a class that does not include the module. What will happen?

Ruby

module Talk
  def speak
    "Speaking"
  end
end

class Animal
end

a = Animal.new
puts a.speak

A NoMethodError: undefined method `speak' for #<Animal:0x000...>

B nil

C SyntaxError: unexpected end-of-input

D Speaking

💡 Hint

Think about whether the class has access to the module's methods without including it.

The Animal class does not include the Talk module, so instances of Animal do not have the speak method. Calling a.speak raises a NoMethodError.

🔧 Debug

advanced

Why does this Ruby code raise an error?

Examine the Ruby code below. It tries to include a module for instance methods, but raises an error. What is the cause?

Ruby

module Friendly
  def greet
    "Hi!"
  end
end

class Robot
  include Friendly()
end

r = Robot.new
puts r.greet

A NameError because Friendly is undefined

B NoMethodError because greet is private

C NoMethodError: undefined method `()' for Friendly:Module

D Works fine and prints "Hi!"

💡 Hint

Look closely at the include Friendly() statement.

The include Friendly() line causes Ruby to evaluate Friendly() as the argument to include. Modules do not define a () method, so it raises NoMethodError: undefined method `()' for Friendly:Module. The correct syntax is include Friendly.

🧠 Conceptual

advanced

How does Ruby's include affect method lookup for instance methods?

In Ruby, when a module is included in a class, how does it affect the method lookup path for instance methods?

A The module's methods override all class methods and become class methods themselves.

B The module is ignored unless explicitly called with the module name.

C The module is copied into the class as class methods only, not instance methods.

D The module is inserted into the class's ancestor chain just above the class, so its instance methods are found before the class's own methods.

💡 Hint

Think about how Ruby searches for methods when you call them on an instance.

Including a module inserts it into the class's ancestor chain just above the class. This means the module's instance methods are found before the class's own methods during method lookup.

❓ Predict Output

expert

What is the output of this Ruby code with multiple includes and method overrides?

Analyze the following Ruby code where a class includes two modules with methods of the same name. What will be printed?

Ruby

module A
  def info
    "Module A"
  end
end

module B
  def info
    "Module B"
  end
end

class MyClass
  include A
  include B
  def info
    "MyClass"
  end
end

obj = MyClass.new
puts obj.info

A MyClass

B Module B

C Module A

D NoMethodError

💡 Hint

Remember that methods defined in the class override included module methods.

The method info defined in MyClass overrides the methods from modules A and B. So calling obj.info prints "MyClass".