Understanding Dependency Injection in PHP

Dependency Injection (DI) is a key principle in modern PHP applications, helping to decouple code and make it more testable.

What is Dependency Injection?

DI allows a class to receive its dependencies from the outside rather than creating them internally:

class UserService {
    private Mailer $mailer;

    public function __construct(Mailer $mailer) {
        $this->mailer = $mailer;
    }

    public function notifyUser(User $user) {
        $this->mailer->send($user->getEmail(), "Hello!");
    }
}

Benefits

• Reduces coupling
• Makes unit testing easier
• Improves maintainability

Implementing DI

Use constructor injection, setter injection, or a DI container. Symfony's Service Container is a popular example.

Conclusion

Understanding and applying DI correctly leads to cleaner, more maintainable, and scalable PHP applications.