Instanceof operator in PHP - Step-by-Step Execution

Concept Flow - Instanceof operator

Create object

↓

Check if object is instance of class/interface

↓

Return true

The instanceof operator checks if an object belongs to a class or implements an interface, returning true or false.

Execution Sample

PHP

<?php
class Animal {}
class Dog extends Animal {}
$dog = new Dog();
var_dump($dog instanceof Animal);
?>

This code checks if the object $dog is an instance of the Animal class or its subclass.

Execution Table

Step	Action	Evaluation	Result
1	Create class Animal	N/A	Class Animal defined
2	Create class Dog extends Animal	N/A	Class Dog defined
3	Create object $dog = new Dog()	N/A	Object $dog created of class Dog
4	Check $dog instanceof Animal	$dog is Dog, Dog extends Animal	bool(true)
5	Output result	bool(true)	bool(true) printed

💡 Instanceof check completes with true because Dog is subclass of Animal

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
$dog	undefined	object of Dog	object of Dog	object of Dog

Key Moments - 2 Insights

Why does $dog instanceof Animal return true even though $dog is created as Dog?

Because Dog is a subclass of Animal, so $dog is considered an instance of Animal too, as shown in execution_table step 4.

What happens if we check an object against an unrelated class?

The instanceof operator returns false, because the object is not an instance of that class or its parents, similar to the 'No' branch in concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the result of $dog instanceof Animal?

A null

B true

C false

D error

💡 Hint

Check the 'Result' column in execution_table row 4.

At which step is the object $dog created?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column for object creation in execution_table.

If Dog did not extend Animal, what would $dog instanceof Animal return?

A false

B true

C null

D error

💡 Hint

Refer to concept_flow where 'No' branch returns false.

Concept Snapshot

Instanceof operator syntax: $object instanceof ClassName
Returns true if $object is instance of ClassName or subclass.
Returns false otherwise.
Used to check object type safely.
Works with classes and interfaces.

Full Transcript

This visual trace shows how the instanceof operator works in PHP. First, classes Animal and Dog are defined, with Dog extending Animal. Then, an object $dog is created from Dog. The operator checks if $dog is an instance of Animal. Because Dog inherits from Animal, the check returns true. The variable $dog holds the Dog object throughout. If checked against an unrelated class, instanceof would return false. This helps safely identify object types in code.