What a container does

• Registers how to build AuthService when someone asks for it.
• May cache one shared ApiClient or create a fresh instance per request.

Manual container (learning shape)

class AppContainer {
  late final ApiClient api;
  late final AuthRepository repo;
  late final AuthService auth;

  AppContainer() {
    api = HttpApiClient(baseUrl: 'https://api.example.com');
    repo = RemoteAuthRepository(api);
    auth = AuthService(repo);
  }
}

void main() {
  final app = AppContainer();
  app.auth.signIn('a@b.com', 'secret');
}

• AppContainer is your composition root: the only place that chooses concrete classes for this run.

Libraries

• get_it is a common Dart service locator / registry that can behave like a container when used with explicit registration.
• Spring-style full containers are rarer in Dart; teams often combine get_it + constructor injection.

Practice tasks

• Split AppContainer into AppContainer.test() that wires fakes and AppContainer.prod() that wires HTTP.
• Add a void dispose() that closes clients if they hold sockets or streams.
• Sketch registration order: which type must exist before AuthService can be constructed?