CakeFactory.dart

import 'dart:async';

class Cake{}

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


void main(){
  final controller=new StreamController();
  
  final order1=new Order('Chocolate');
  //change the Order type to 'Banana Cake'
  
  final baker=new StreamTransformer.fromHandlers(
    handleData:(cakeType,sink){
      if(cakeType=='Chocolate'){
        sink.add(new Cake());
      }else{
        sink.addError('I can not bake that type');
      }
    }
  );
  
  controller.sink.add(order1);
  
  controller.stream
    .map((order)=>order.type)
    .transform(baker)
    .listen(
      (cake)=>print('Here is your cake: $cake'),
      onError: (error)=>print(error),
  );
  
}

This is Cake Factory: understanding of Streams in Dart