Minimize mutability

Wherever possible, use constructor injection to create immutable objects. Immutable objects are simple, shareable, and can be composed. Follow this pattern to define your injectable types:

class RealPaymentService implements PaymentServiceInterface
{
    public function __construct(
        private readnonly PaymentQueue $paymentQueue,
        private readnonly Notifier $notifier;
    ){}

All fields of this class are readonly and initialized by a constructor.

Injecting methods

Constructor injection has some limitations:

• Injected constructors may not be optional.
• It cannot be used unless objects are created by Ray.Di.
• Subclasses must call parent() with all dependencies. This makes constructor injection cumbersome, especially as the injected base class changes.

Setter injection is most useful when you need to initialize an instance that is not constructed by Ray.Di.