Explain dependency injection in PHP and its benefits.

Dependency injection is a design pattern where dependencies are provided to a class rather than the class creating them itself.\n\nBenefits:\n- Loose coupling\n- Easier testing\n- Better maintainability\n- Follows SOLID principles\n\nExample:\nclass EmailService {\n public function send($message) { /* ... */ }\n}\n\nclass UserController {\n private $emailService;\n \n public function __construct(EmailService $emailService) {\n $this->emailService = $emailService;\n }\n}\n\n// Dependency is injected\n$controller = new UserController(new EmailService());