Interface Segregation Principle (ISP)

Interface Segregation Principle (ISP)

this topic is easy to understand and help us to develop code with loose coupled and more reusable

🔹 Understand ISP

👉 Definition:
Clients should not be forced to depend on interfaces they do not use.

A fat interface = an interface with too many methods.

A role-specific interface = smaller, focused interfaces.

⚠️ Violation Example (fat interface):

interface Worker {
    public function work();
    public function eat();
    public function sleep();
}

class Robot implements Worker {
    public function work() {
        echo "Robot is working";
    }

    // ❌ Robot doesn’t eat or sleep, but is forced to implement these
    public function eat() {
        throw new Exception("Robots don’t eat");
    }

    public function sleep() {
        throw new Exception("Robots don’t sleep");
    }
}

💡 Problem: Robot depends on methods it doesn’t need → ISP violation.

✅ Fix with role interfaces:

interface Workable {
    public function work();
}

interface Eatable {
    public function eat();
}

interface Sleepable {
    public function sleep();
}

class Human implements Workable, Eatable, Sleepable {
    public function work() { echo "Human works"; }
    public function eat() { echo "Human eats"; }
    public function sleep() { echo "Human sleeps"; }
}

class Robot implements Workable {
    public function work() { echo "Robot works"; }
}

Now, each class only implements what it needs 👍

🔹 Refactor Example in Laravel

Let’s apply ISP in a Laravel context.

⚠️ Bad (Fat Interface):

interface NotificationInterface {
    public function sendEmail($message);
    public function sendSMS($message);
    public function sendPush($message);
}

class EmailNotification implements NotificationInterface {
    public function sendEmail($message) { echo "Email: $message"; }
    public function sendSMS($message) { throw new Exception("Not supported"); }
    public function sendPush($message) { throw new Exception("Not supported"); }
}

✅ Good (Role Interfaces):

interface EmailNotifiable {
    public function sendEmail($message);
}

interface SMSNotifiable {
    public function sendSMS($message);
}

interface PushNotifiable {
    public function sendPush($message);
}

class EmailNotification implements EmailNotifiable {
    public function sendEmail($message) { echo "Email: $message"; }
}

class SMSNotification implements SMSNotifiable {
    public function sendSMS($message) { echo "SMS: $message"; }
}

class PushNotification implements PushNotifiable {
    public function sendPush($message) { echo "Push: $message"; }
}