usecasesample1.dart

  //Usecase Implementation
  class PostBillingInfoUseCase
    extends UseCase<BillingInfoRequest, BillingInfoResponse> {
  final BillingInfoRepository _billingInfoRepository;

  PostBillingInfoUseCase(this._billingInfoRepository);

  @override
  Stream<BillingInfoResponse> buildUseCase(BillingInfoRequest param) {
    return _billingInfoRepository.postBillingInfo(param).asStream();
  }
}
  //Usecase invocation from presentation layer
  PostBillingInfoUseCase(MockedBillingInfoRepository())
      .execute(BillingInfoRequest(), (result) {
    //TODO Display result
  }, (errorMessage) {
    //TODO Display error
  });

//Usecase implementation
class PostShippingInfoUseCase extends UseCase<ShippingInfoRequest, ShippingInfoResponse> {
  final ShippingInfoRepository _shippingInfoRepository;

  PostShippingInfoUseCase(this._shippingInfoRepository);

  @override
  Stream<ShippingInfoResponse> buildUseCase(ShippingInfoRequest param) {
    return _shippingInfoRepository.postShippingInfo(param).asStream();
  }
}

  //Usecase invocation from presentation layer
  PostShippingInfoUseCase(MockedShippingInfoRepository())
  .execute(ShippingInfoRequest(), (result) {
    //TODO Display result
  }, (errorMessage) {
    //TODO Display result
  });

  //Usecase implementation
  class PostBillingAndShippingInfoUseCase
    extends UseCase<BillingShippingInfoRequest, BillingShippinInfoResponse> {
  final PostBillingInfoUseCase _postBillingInfoUseCase;
  final PostShippingInfoUseCase _postShippingInfoUseCase;

  PostBillingAndShippingInfoUseCase(
      this._postBillingInfoUseCase, this._postShippingInfoUseCase);

  @override
  Stream<BillingShippinInfoResponse> buildUseCase(
      BillingShippingInfoRequest param) {
    return Rx.zip2(
        _postBillingInfoUseCase.buildUseCase(param.billingInfoRequest),
        _postShippingInfoUseCase.buildUseCase(param.shippingInfoRequest),
        (BillingInfoResponse billingResult,
                ShippingInfoResponse shippingResult) =>
            BillingShippinInfoResponse.from(billingResult, shippingResult));
    }
  }

  //Usecase invocation from presentation layer
  PostBillingAndShippingInfoUseCase(PostBillingInfoUseCase(MockedBillingInfoRepository()),PostShippingInfoUseCase(MockedShippingInfoRepository()))
      .execute(BillingShippingInfoRequest(BillingInfoRequest(),ShippingInfoRequest()), (result) {
    //TODO Display result
  }, (errorMessage) {
    //TODO Display result
  });