Type checking with .class and .is_a? in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the .class method do in Ruby?

It returns the exact class of an object. For example, <code>5.class</code> returns <code>Integer</code>.

intermediate

What is the difference between .class and .is_a? in Ruby?

<code>.class</code> checks the exact class of an object, while <code>.is_a?</code> checks if the object is an instance of a class or any of its parent classes (inheritance).

intermediate

How does .is_a? help with inheritance?

It returns <code>true</code> if the object is an instance of the given class or any class it inherits from, making it useful to check for types in a family of classes.

beginner

Example: What is the output of "hello".class and "hello".is_a?(String)?

The output of "hello".class is String. The output of "hello".is_a?(String) is true.

intermediate

Can .is_a? return true for a superclass?

Yes, <code>.is_a?</code> returns <code>true</code> if the object is an instance of the class or any of its superclasses.

What does obj.class return in Ruby?

A Whether obj is a string

B True if obj is a class

C The superclass of obj

D The exact class of obj

.class returns the exact class of the object.

Which method checks if an object is an instance of a class or its parent classes?

A .is_a?

B .class

C .to_s

D .superclass

.is_a? checks for the class or any superclass.

What will 5.is_a?(Numeric) return?

A false

B nil

C true

D error

5 is an Integer, which inherits from Numeric, so .is_a?(Numeric) returns true.

If obj.class == String is true, what does obj.is_a?(Object) return?

A false

B true

C nil

D error

All classes in Ruby inherit from Object, so .is_a?(Object) returns true.

Which method would you use to check if an object is exactly a certain class, not a subclass?

A .instance_of?

B .kind_of?

C .is_a?

D .class

.instance_of? checks if the object is exactly that class, not subclasses.

Explain the difference between .class and .is_a? in Ruby with examples.

Think about checking exact type vs family of types.

How can you use .is_a? to safely check an object's type in a program?

Consider when you want to accept objects of related types.