some_repository_full.dart

class SomeRepository implements ISomeRepository {
    SomeRepository({
        required ILocalDataSource localDataSource,
        required IRemoteDataSource remoteDataSource,
    }) :  _localDataSource = localDataSource,
          _remoteDataSource = remoteDataSource;

    final ILocalDataSource _localDataSource;
    final IRemoteDataSource _remoteDataSource;

    @override
    Future<SomeModel> getModel(int modelId) async {
      try {
        final model = await _remoteDataSource.getModel(modelId);
        await _localDataSource.saveModel(model);
        return model;
      } catch (e) {
        // si el llamado al API falla...
        try {
          final model = _localDataSource.getSavedModel();
          return model;
        } catch (e) {
          throw CacheError();
        }
      }
    }
}