effect-layers-services

Dependency injection with swappable implementations uses service layers to bind live and test versions at app startup. Define service interfaces, create Live and Test layers that provide concrete implementations, and compose them at your app boundary. This lets you switch between environments without code changes.

Structure services by defining clear interfaces, then provide implementations through dependency injection layers. Separate live implementations (database, HTTP clients, loggers) from test doubles in distinct layers. This boundary makes tests predictable and fast while keeping production code unchanged.

Compose layers by declaring service interfaces, creating provider layers for each environment (live, test), and combining them at your app's entry point. Each layer binds concrete implementations to interfaces. The composition establishes your app-wide infrastructure boundaries for loggers, databases, and HTTP clients.

Yes. Service layers enable environment-aware provision through swappable bindings. Define a service interface once, provide live implementation in production and test doubles in tests, then pass the appropriate layer to your app. No code duplication or environment-specific logic needed.

Apply DI boundaries when building scalable apps requiring infrastructure components like loggers, databases, and HTTP clients. Service layers work best for app-wide composition where you need predictable testing, clear separation of concerns, and the ability to swap implementations across environments.