@immutable
class StreamWidget<T> extends StatelessWidget {
  final Stream<T> stream;
  final DataBuilder<T> builder;
  final LoadingBuilder loadingBuilder;
  final ErrorBuilder errorBuilder;

  StreamWidget(
      {@required this.stream,
      @required this.builder,
      this.loadingBuilder,
      this.errorBuilder});

  @override
  Widget build(BuildContext context) =>
      StreamBuilder<T>(builder: (context, snapshot) {
        if (snapshot.hasError) {
          return errorBuilder != null
              ? errorBuilder(context, snapshot.error)
              : Container();
        }

        if (!snapshot.hasData) {
          return loadingBuilder != null ? loadingBuilder(context) : Container();
        }

        builder(context, snapshot.data);
      });
}

class MyFancyWidget extends StatefulWidget {
  @override
  _MyFancyWidgetState createState() => _MyFancyWidgetState();
}

class _MyFancyWidgetState extends State<MyFancyWidget> {
  @override
  Widget build(BuildContext context) {
    return StreamWidget<String>(
        stream: Observable.just("Hello!").delay(Duration(seconds: 2)),
        loadingBuilder: (context) => CircularProgressIndicator(),
        builder: (context, message) => Text(message));
  }
}