Is_a? and kind_of? for type checking in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the is_a? method do in Ruby?

It checks if an object is an instance of a given class or one of its subclasses. It returns <code>true</code> if yes, otherwise <code>false</code>.

beginner

Is there any difference between is_a? and kind_of? in Ruby?

No, both methods do the same thing. They check if an object belongs to a class or its subclass. They are interchangeable.

beginner

How would you check if the variable <code>obj</code> is a String or a subclass of String?

You can use obj.is_a?(String) or obj.kind_of?(String). Both return true if obj is a String or inherits from String.

beginner

What will 5.is_a?(Numeric) return and why?

It returns <code>true</code> because <code>5</code> is an Integer, and Integer is a subclass of Numeric.

beginner

Why is type checking with is_a? useful in Ruby?

It helps you confirm the kind of object you have before calling methods on it, preventing errors and making your code safer.

What does obj.is_a?(ClassName) check in Ruby?

A If obj is an instance of ClassName or its subclass

B If obj is exactly ClassName, no subclasses

C If obj is a method of ClassName

D If obj is a variable named ClassName

is_a? returns true if the object is an instance of the class or any subclass.

Which method is equivalent to is_a? in Ruby?

A kind_of?

B instance_of?

C respond_to?

D class

kind_of? does the same type check as is_a?.

What will "hello".is_a?(String) return?

A nil

B false

C true

D error

The string "hello" is an instance of String, so it returns true.

What is the difference between is_a? and instance_of??

A Neither checks class

B <code>instance_of?</code> checks exact class, <code>is_a?</code> includes subclasses

C They are exactly the same

D <code>is_a?</code> checks exact class, <code>instance_of?</code> includes subclasses

instance_of? returns true only if the object is exactly that class, not subclasses.

If num = 10, what does num.is_a?(Integer) return?

A nil

B false

C error

D true

10 is an Integer, so it returns true.

Explain how is_a? and kind_of? work for type checking in Ruby.

Think about how Ruby checks if an object belongs to a class or its children.

Describe a situation where using is_a? would help prevent errors in Ruby code.

Imagine you want to call a method only if the object is a string.