Injection & inheritance

Compose by default for multiple operations

An operation field keeps execution reusable without occupying a superclass slot. It also lets a store hide mutation behind domain methods. Extend an operation when reusable behavior belongs to the operation itself, for example a MobX read/change bridge.

class TracedOperation<T> extends AsyncOperation<T> {
  TracedOperation({super.initialState, super.concurrency, super.errorMessage});

  @override
  void onChanged(OperationState<T> previous, OperationState<T> next) {
    super.onChanged(previous, next);
    trace(next);
  }
}

The example assumes an application-defined trace function. Forward the constructor options your adapter intends to support. A minimal subclass does not automatically expose every base constructor option.

Cubit, ChangeNotifier, and Notifier already occupy the superclass slot. MobX Store is a mixin and can accompany an operation superclass. See MobX.

Inject through operationController

class UserStore with AsyncOperationMixin<User> {
  UserStore(this.repository, this.operationController);
  final UserRepository repository;

  @override
  final AsyncOperation<User> operationController;

  @override
  Future<User> fetch() => repository.fetchUser();
}

The injected engine is owned by the receiving store. Its inherited commands, state reads, message attachment, and disposeOperation route through operationController. The default lazy engine is never constructed when this getter is overridden.

Configure callbacks, concurrency, error formatting, and initial state on the supplied engine. Host hooks are wired only by the default controller implementation. Injection does not automatically attach operationChanged, operationRead, or lifecycle callbacks.

Return one stable instance during a host lifetime. Never create a new engine per getter read. Overriding only operation changes state reads but leaves commands routed through the original controller. Override operationController to replace both. Do not share one owned engine among multiple disposing hosts.

The same controller contract applies to StreamOperationMixin. A Riverpod build boundary may legitimately replace a controller for a new lifetime; it must dispose the exact old instance. See Riverpod.