Inheritance vs. Composition in PHP

When writing code, two big ideas pop up: inheritance and composition. These ideas help us organize and reuse code. But what are they? Let’s break them down in simple terms.

Inheritance is like a family tree. A class (child) gets all the traits from another class (parent). It’s a way to reuse code.

For example:

class Animal {
    public function makeSound() {
        echo "Some sound";
    }
}

class Dog extends Animal {
    // Dog gets the makeSound method from Animal
}

In this example, the Dog class gets the makeSound method from the Animal class. This means we don’t have to write the same code twice.

Pros of Inheritance:

• Code reuse: You write a method once and use it in many classes.
• Easy to understand: It’s like a family tree where the child inherits traits.

Cons of Inheritance:

• Tight coupling: The child class is linked to the parent. Changes in the parent class can affect the child.
• Hard to scale: As your code grows, inheritance trees can become confusing.

Composition is when one class uses another class inside it. Instead of a child inheriting from a parent, one class includes another as a part of it. It’s like building something with blocks.

For example:

class Engine {
    public function start() {
        echo "Engine started";
    }
}

class Car {
    public function __construct(private Engine $engine) {
    }

    public function startCar() {
        $this->engine->start();
    }
}

$car = new Car(new Engine());
$car->startCar(); // Outputs: Engine starts

Here, the Car class uses an Engine object. It doesn’t inherit from Engine. Instead, it builds a relationship through composition.

Pros of Composition:

• Flexible: You can easily swap parts (like swapping the engine) without changing the entire class.
• Easier to scale: Adding new features is simple because parts are independent.
• Unit Testing: Unit testing is easy in composition because we know what all methods we are using from another class.

Cons of Composition:

• More setup: You may need to write more code to set things up.
• Can be harder to follow: For beginners, using many classes together might feel confusing.

• Use inheritance when classes are in a clear parent-child relationship. Example: Dog inherits from Animal.
• Use composition when you need flexibility and want to build things in parts. Example: A Car can use different engines without changing how it works.

Both inheritance and composition help us write cleaner code. Inheritance works when you need a clear family tree of classes. Composition is better for building things that need flexibility. Pick the right one based on your needs!