Dart async

main.dart

import 'dart:async';
import 'dart:math';

//https://www.dartlang.org/articles/language/beyond-async
void main() async {
  
  //final stocksSync = StocksService().stocksSync();
  //print(stocksSync);
  //final stocksAsync = await StocksService().stocksAsync();
  //print(stocksAsync);
  //StocksService().stocksAsync().then((stocks) => print(stocks));
  
  //StocksService().stockStream('orange').listen((stock) => print(stock));
  //StocksService().stockStream('orange').where((stock) => stock.price > 3.0).listen((stock) => print(stock));
  
  Stream<String> descStream=StocksService().stockStream('orange').map((stock) => 'Mapped Desc: ${stock.name} is currently ${stock.price}');
  descStream.listen((desc) => print(desc));
}


class StocksService {
  final List<Stock> _stocks = [Stock(name: 'orange', price: 12), Stock(name: 'google', price: 9.0)];
  
  List<Stock> stocksSync() {
    return _stocks;
  }
  
  Future<List<Stock>> stocksAsync() async {
    await Future.delayed(Duration(seconds: 5));
    return _stocks;
  }
  
  Stream<Stock> stockStream(String name) async*{
    for (int i = 0; i < 100; i++) { 
    	await Future.delayed(Duration(seconds: 5));
      yield Stock(name: name, price: Random().nextDouble()*10);
    }
  }
  
}

class Stock {
  final String name;
  final double price;
  
  Stock({this.name, this.price});
  
  factory Stock.fromMap(Map<String, dynamic> map) {
    return Stock(name: map['name'], price: map['price']);
  }
  
  @override
  String toString() {
    return '$name, $price';
  }
}