Explain Dependency Injection in Laravel.

In Laravel, dependency injection (DI) is a way for classes to receive their dependencies from external sources rather than creating them internally by the class.

🔹 Simple Idea

Instead of doing this ❌:

class UserController {
    public function index() {
        $service = new UserService(); // tightly coupled
    }
}

We do this ✅:

class UserController {
    protected $service;

    public function __construct(UserService $service) {
        $this->service = $service; // injected automatically
    }
}

👉 Laravel automatically creates and injects UserService using its Service Container.

🔹 Why Use Dependency Injection?

1. Loose Coupling

Your code doesn’t depend on a specific implementation.

2. Easy Testing

You can replace real classes with mock objects.

3. Cleaner Code

No need to manually create objects everywhere.

🔹 How Laravel Handles DI

Laravel uses a Service Container to resolve dependencies automatically.

Example: Controller Injection

use App\Services\UserService;

class UserController extends Controller
{
    public function __construct(UserService $userService)
    {
        $this->userService = $userService;
    }
}

🔹 Method Injection (Very Common in Laravel)

public function store(Request $request, UserService $service)
{
    $service->create($request->all());
}

👉 Laravel injects both:

• Request
• UserService

🔹 Binding in Service Container

Sometimes you bind interfaces to implementations.

$this->app->bind(
    PaymentInterface::class,
    RazorpayService::class
);

Now Laravel knows:

When PaymentInterface is needed → use RazorpayService

🔹 Real-World Example

interface PaymentInterface {
    public function pay($amount);
}

class RazorpayService implements PaymentInterface {
    public function pay($amount) {
        return "Paid via Razorpay";
    }
}

class OrderController {
    public function checkout(PaymentInterface $payment) {
        return $payment->pay(1000);
    }
}

👉 Laravel injects RazorpayService automatically.

🔹 Types of Dependency Injection in Laravel

1. Constructor Injection (most common)
2. Method Injection
3. Interface Injection (via binding)