Service Providers & Dependency Injection

Service Providers

Service providers are the central place to register application services, bindings, and event listeners. They are stored in app/Providers.

Use service providers to bind interfaces to implementations, register singletons, and configure third-party packages.
Split custom logic into multiple providers for clarity (e.g., AppServiceProvider, AuthServiceProvider, EventServiceProvider).
Register providers in config/app.php under the providers array.

Example: Registering a binding

public function register()
{
    $this->app->bind(UserRepositoryInterface::class, UserRepository::class);
}

Dependency Injection

Dependency injection allows you to automatically resolve class dependencies. Use constructor injection for controllers, services, and jobs.

Prefer interfaces for type-hinting to allow flexibility and easier testing.
Use Laravel's automatic resolution for dependencies in controllers and jobs.

Example: Controller injection

class UserController extends Controller
{
    protected $users;
    public function __construct(UserRepositoryInterface $users)
    {
        $this->users = $users;
    }
}

Singleton vs Transient

Register singletons for shared services that should only have one instance per request lifecycle:
```
$this->app->singleton(CacheService::class, function ($app) {
  return new CacheService();
});
```

$this->app->bind(NotificationService::class, function ($app) {
  return new NotificationService();
});

Best Practices

Use dependency injection for all services and repositories.
Avoid using the app() helper or service container directly in controllers.
Document service provider logic with comments.
Use interfaces for all injected dependencies to improve testability.
Keep service providers focused and avoid mixing unrelated logic.

Example: Custom Service Provider

class CustomServiceProvider extends ServiceProvider
{
    public function register()
    {
        $this->app->singleton(CustomService::class, function ($app) {
            return new CustomService();
        });
    }
    public function boot()
    {
        // Boot logic, e.g., event listeners
    }
}