chocolate-factory-stream.dart

import 'dart:async';

class Cake {
}

class Order {
  String type;
  
  Order(this.type);
}

void main() {
  final controller = new StreamController();
  final order = new Order('chocolate');
  final baker = new StreamTransformer.fromHandlers(
    handleData: (cakeType, sink) {
      if (cakeType == 'chocolate') {
        sink.add(new Cake());
      } else {
        sink.addError('I can not bake that type: $cakeType');
      }
    }
  );
  
  controller.sink.add(order);
  
  controller.stream
    .map((order) {
      return order.type;
    })
    .transform(baker)
    .listen(
      (cake) => print('Here is your $cake'),
      onError: (error) => print(error)
    );
}