Type checking with .class and .is_a? in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of .class vs .is_a? for Integer

What is the output of the following Ruby code?

Ruby

num = 42
puts num.class
puts num.is_a?(Integer)

A

Integer
true

B

Integer
false

C

Fixnum
true

D

Fixnum
false

💡 Hint

Remember Ruby 2.4+ unified Fixnum and Bignum into Integer.

The .class method returns the exact class of the object, which is Integer in modern Ruby versions.

The .is_a?(Integer) method checks if the object is an instance of Integer or its subclasses, so it returns true.

❓ Predict Output

intermediate

Checking class inheritance with .is_a?

What will this Ruby code print?

Ruby

class Animal; end
class Dog < Animal; end
pet = Dog.new
puts pet.class
puts pet.is_a?(Animal)

A

Dog
true

B

Animal
true

C

Dog
false

D

Animal
false

💡 Hint

Remember that .class returns the object's exact class, but .is_a? checks inheritance.

pet.class returns Dog because pet is an instance of Dog.

pet.is_a?(Animal) returns true because Dog inherits from Animal.

🔧 Debug

advanced

Why does this .is_a? check fail?

Consider this Ruby code snippet. Why does the .is_a? check return false?

Ruby

class Vehicle; end
class Car < Vehicle; end
my_car = Vehicle.new
puts my_car.is_a?(Car)

A Because Car is not defined properly as a subclass

B Because .is_a? only works with modules, not classes

C Because my_car is an instance of Vehicle, not Car or its subclass

D Because .is_a? checks exact class equality, not inheritance

💡 Hint

Think about the object and class relationship and what .is_a? means.

my_car is an instance of Vehicle, not Car. The .is_a?(Car) method returns true only if the object is an instance of Car or its subclasses.

📝 Syntax

advanced

Identify the syntax error in type checking

Which option contains a syntax error when checking an object's type in Ruby?

Ruby

obj = 'hello'

A obj.is_a?(String)

B obj.is_a?(String))

C obj.class == String

D obj.class.eql?(String)

💡 Hint

Check for unmatched parentheses.

Option B has an extra closing parenthesis, causing a syntax error.

Other options are syntactically correct ways to check type.

🚀 Application

expert

Determine the output of complex type checks

What is the output of this Ruby code?

Ruby

module Mixin; end
class Parent; include Mixin; end
class Child < Parent; end
obj = Child.new
puts obj.is_a?(Mixin)
puts obj.class == Parent
puts obj.is_a?(Parent)

A

false
false
true

B

true
true
true

C

true
false
false

D

true
false
true

💡 Hint

Remember that .is_a? checks inheritance and included modules, but .class checks exact class.

obj.is_a?(Mixin) is true because Parent includes Mixin and Child inherits Parent.

obj.class == Parent is false because obj's class is Child, not Parent.

obj.is_a?(Parent) is true because Child inherits Parent.