Stack (typical)

• get_it: service locator registry (GetIt.instance).
• injectable: annotations that describe how to register each class.
• build_runner: generates dependency_injection.config.dart (name may vary with version) that calls GetIt registration functions.

Shape (conceptual)

@injectable
class AuthService {
  AuthService(this._client, this._repo);
  final ApiClient _client;
  final AuthRepository _repo;
}

• Codegen discovers constructors and dependency types, then emits registration code so you do not hand-write every registerSingleton.

Where it fits

• Medium and large graphs with many implementations and environments (dev, prod, test).
• Teams that want compile-time checks on constructor lists and less merge conflict in one giant setup() file.

Costs

• Build step: dart run build_runner build --delete-conflicting-outputs.
• Learning curve when generated files disagree with manual edits.

Practice tasks

• Read the injectable readme on pub.dev and note three annotations (@singleton, @lazySingleton, @injectable, etc.).
• Start a throwaway package, add get_it + injectable, generate once, and diff the output file.
• Decide one rule: “no GetIt.I inside domain classes” and enforce in review.