How does Rails handle large-scale dependency injection and service composition?

Rails uses manual dependency injection or libraries like Dry-Rb to decouple service dependencies.

Dependency injection (DI) allows Rails services to receive dependencies externally rather than creating them internally. This improves testability and flexibility. In large systems, DI containers or patterns like constructor injection are used. It allows swapping implementations (e.g., mock services in tests or different payment providers in production).