Introduction: Why PHP Inheritance Is Essential

As your application grows, repeating similar code across classes becomes a problem. It leads to bloated codebases, harder maintenance, and bugs. PHP Inheritance offers a solution by allowing you to reuse and extend existing class functionality.

Inheritance is a core concept in Object-Oriented Programming (OOP). It allows a class (child or subclass) to inherit properties and methods from another class (parent or base class), promoting cleaner, DRY (Don't Repeat Yourself) code.

What Is Inheritance in PHP?

Inheritance allows one class to adopt the behavior (methods) and properties (variables) of another. PHP uses the extends keyword to declare a child class that inherits from a parent.

Syntax:

class ParentClass {
    // parent methods and properties
}

class ChildClass extends ParentClass {
    // additional methods and properties
}

Step-by-Step: PHP Inheritance Explained

Step 1: Create the Parent Class

The parent class defines common behavior or properties that multiple child classes can share.

class Animal {
    public $name;

    public function makeSound() {
        echo "Some generic sound\n";
    }
}

Step 2: Extend the Parent Class with extends

The child class uses the extends keyword to inherit from the parent.

class Dog extends Animal {
    public function makeSound() {
        echo "Woof!\n"; // Overrides the parent method
    }
}

Step 3: Use the Inherited Methods and Properties

$dog = new Dog();
$dog->name = "Buddy";
echo $dog->name . "\n";  // Output: Buddy
$dog->makeSound();       // Output: Woof!

Complete Functional Code Example

<?php
class Vehicle {
    public $brand;

    public function startEngine() {
        echo "Engine started for {$this->brand}\n";
    }
}

class Car extends Vehicle {
    public $model;

    public function carDetails() {
        echo "Car: {$this->brand} {$this->model}\n";
    }
}

$car = new Car();
$car->brand = "Toyota";
$car->model = "Corolla";
$car->startEngine();     // Inherited method
$car->carDetails();      // Child method
?>

⚠️ Tips & Common Pitfalls

✅ Best Practices

• Use inheritance for “is-a” relationships (e.g., a Dog is an Animal).

• Keep the parent class generalized, and extend functionality in child classes.

• Leverage parent::method() if you want to use the parent version inside the child method.

❌ Common Mistakes

• Overusing inheritance when composition might be more appropriate.

• Not marking parent methods as protected or public—which prevents access in child classes.

• Forgetting that private properties and methods are not inherited.

Comparison Table: Access to Members

Key Concepts in PHP Inheritance

Method Overriding

Child classes can override methods from the parent.

class Cat extends Animal {
    public function makeSound() {
        echo "Meow!\n";
    }
}

Calling the Parent Method

You can still access the parent’s version using parent::.

class Truck extends Vehicle {
    public function startEngine() {
        parent::startEngine(); // Call parent method
        echo "Truck engine warmed up.\n";
    }
}

Conclusion: Writing Cleaner PHP with Inheritance

PHP inheritance allows developers to create modular, scalable, and maintainable applications. By structuring your code with parent and child classes, you reduce duplication and increase readability.

Takeaways:

• Use extends to implement inheritance in PHP.

• Override parent methods when specific behavior is needed.

• Avoid inheritance overuse—sometimes composition is better.

• Always keep OOP principles like encapsulation and polymorphism in mind.