Is_a? and kind_of? for type checking in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of is_a? with inheritance

What is the output of this Ruby code snippet?

Ruby

class Animal; end
class Dog < Animal; end

fido = Dog.new
puts fido.is_a?(Animal)

A true

B false

C nil

D TypeError

💡 Hint

Remember that is_a? returns true if the object is an instance of the class or its subclass.

The Dog class inherits from Animal. So, fido.is_a?(Animal) returns true because fido is an instance of Dog, which is a subclass of Animal.

❓ Predict Output

intermediate

kind_of? method behavior

What will this Ruby code print?

Ruby

arr = [1, 2, 3]
puts arr.kind_of?(Array)
puts arr.kind_of?(Object)

A true\nfalse

B true\ntrue

C false\ntrue

D false\nfalse

💡 Hint

kind_of? behaves like is_a? and checks inheritance.

arr is an instance of Array, so arr.kind_of?(Array) is true. Since Array inherits from Object, arr.kind_of?(Object) is also true.

❓ Predict Output

advanced

Difference between is_a? and kind_of?

What is the output of this Ruby code?

Ruby

class Vehicle; end
class Car < Vehicle; end

car = Car.new
puts car.is_a?(Vehicle)
puts car.kind_of?(Vehicle)

A true\ntrue

B true\nfalse

C false\ntrue

D false\nfalse

💡 Hint

Both methods check the same inheritance chain.

In Ruby, is_a? and kind_of? are synonyms. Both return true if the object is an instance of the class or its subclass.

❓ Predict Output

advanced

Checking type with is_a? for modules

What will this Ruby code output?

Ruby

module Flyable; end
class Bird
  include Flyable
end

sparrow = Bird.new
puts sparrow.is_a?(Flyable)

A NoMethodError

B false

C true

D TypeError

💡 Hint

is_a? returns true if the object includes the module.

The Bird class includes the Flyable module. So, sparrow.is_a?(Flyable) returns true.

❓ Predict Output

expert

Output of is_a? with singleton class

What does this Ruby code print?

Ruby

obj = Object.new
class << obj
  def greet; 'hello'; end
end

puts obj.is_a?(Object)
puts obj.is_a?(Class)

A true\ntrue

B false\nfalse

C false\ntrue

D true\nfalse

💡 Hint

Singleton class does not change the object's class type.

The object obj is still an instance of Object, so obj.is_a?(Object) is true. It is not an instance of Class, so obj.is_a?(Class) is false.