Type checking with .class and .is_a? in Ruby - Step-by-Step Execution

Concept Flow - Type checking with .class and .is_a?

Start with an object

↓

Check object.class

↓

Compare with a class

↓

Action if exact class

+--No-->↓

Check object.is_a?(Class)

↓

Action if object is instance or subclass

↓

Action if not matching type

↓

End

We first check the exact class of an object using .class, then check if it is an instance of a class or its subclass using .is_a?.

Execution Sample

Ruby

num = 5
puts num.class
puts num.is_a?(Integer)
puts num.is_a?(String)

This code shows how to check the exact class and type membership of a number.

Execution Table

Step	Expression	Evaluation	Result	Explanation
1	num = 5	Assign 5 to num	num = 5	num now holds the integer 5
2	num.class	Check exact class of num	Integer	num is exactly an Integer
3	num.is_a?(Integer)	Check if num is Integer or subclass	true	num is an Integer, so true
4	num.is_a?(String)	Check if num is String or subclass	false	num is not a String, so false

💡 All checks done, program ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
num	undefined	5	5	5	5

Key Moments - 2 Insights

Why does num.class == Integer return true but num.is_a?(Integer) can also be true for subclasses?

num.class returns the exact class, so it must match exactly. num.is_a?(Integer) returns true if num is an instance of Integer or any subclass, so it is more flexible (see execution_table rows 2 and 3).

Can .is_a? return false even if .class matches?

No, if .class matches exactly, .is_a? will always return true because the object is an instance of that class (see execution_table rows 2 and 3).

Visual Quiz - 3 Questions

Look at the execution table, what is the result of num.class at step 2?

A true

B String

C Integer

D false

💡 Hint

Check the 'Result' column in execution_table row 2

At which step does num.is_a?(Integer) return true?

A Step 3

B Step 2

C Step 4

D None

💡 Hint

Look at the 'Expression' and 'Result' columns in execution_table row 3

If num was a String, what would num.is_a?(Integer) return?

A true

B false

C Integer

D Error

💡 Hint

Refer to execution_table row 4 where num is not a String and returns false

Concept Snapshot

Type checking in Ruby:
- Use obj.class to get exact class
- Use obj.is_a?(Class) to check if obj is instance or subclass
- .class == Class checks exact match
- .is_a? returns true for subclasses too
- Useful for flexible type checks

Full Transcript

This visual execution shows how Ruby checks types using .class and .is_a?. First, an object num is assigned the value 5. Checking num.class returns Integer because 5 is exactly an Integer. Using num.is_a?(Integer) returns true because num is an instance of Integer or its subclass. Checking num.is_a?(String) returns false because num is not a String. The difference is .class checks exact class, while .is_a? checks class or subclass membership. This helps decide how to handle objects based on their type.