Future & Stream in Dart

2013 Future & Stream in Dart

Transcript

1. Future & Stream
   in Dart
   tomochikahara
   @zetta1985
   

   View Slide

2. Agenda
   ● Future API
   ● Stream API
   

   View Slide

3. Future API
   for Ansynchronous Programming
   

   View Slide

4. What is a Future?
   ● 「先物」
   ○ 別名Promise。
   ○ 処理結果を必要となる時点まで保持する
   ○ 並列処理のデザインパターン
   ■ Dartでは非同期なだけで並列処理は必須でない
   ● Futureの値を決めるCompleter
   ○ Futureはあくまでも値を保持するのみ
   ○ 計算結果をFutureに与えるのがCompleter
   ● dart:io, indexed_dbなどで利用
   

   View Slide

5. Future & Completer
   Completer
   Future
   Future
   Caller Callee
   Future echoToMountain(String yo_ho);
   call echoToMountain
   create
   get
   Future
   return Future
   then((reply) => catchMyEar(reply))
   complete(reply)
   Execution
   

   View Slide

6. Future & Completer
   import "dart:async";
   Future echoToMountain(String yo_ho) {
   var completer = new Completer();
   new Timer(new Duration(milliseconds: 5000), () {
   completer.complete(yo_ho);
   });
   return completer.future;
   }
   void main() {
   print("before echoToMountain");
   var future = echoToMountain("YooooHooooo");
   future.then(print);
   print("after echoToMountain");
   }
   

   View Slide

7. Future Example
   new File("./foo.txt").fullPath()
   .then((fullpath) {
   print("foo.txt's fullpath is $fullpath");
   })
   .catchError((e) {
   print("foo.txt is not exists.");
   });
   File IO
   (Async try-catch)
   HTTP
   Request
   (Async Process Chain)
   var uri = Uri.parse("http://tomochikahara.com");
   new HttpClient().getUrl(uri)
   .then((HttpClientRequest req){
   // prepare request
   req.headers.add("contentType", "text/html");
   return req.close();
   }).then((HttpClientResponse res) {
   res.transform(new StringDecoder()).forEach(print);
   });
   

   View Slide

8. Stream API
   for sequence of any data
   

   View Slide

9. What is a Stream?
   ● イベントの「流れ」
   ○ 単なる遅延リスト。
   ○ 何回も使えるFuture。
   ○ 値が発すること＝イベント、と表現
   ○ Producer - Consumer Pattern
   ■ Dartでは非同期なだけで並列処理は必須でない
   ● DOM EventやByte IO、標準入力などで利用
   

   View Slide

10. Stream
    What is a Stream?
    Controller
    (Sink)
    Subscription
    D C B' A' ・・・
    Transformer
    F E
    add
    listen
    

    View Slide

11. Stream
    var controller = new StreamController();
    controller.add("A");
    var stream = controller.stream;
    stream.listen((str) => print(str),
    onError : (e) => print("Error"),
    onDone : () => print("Done"));
    controller.add("B");
    controller.add("C");
    controller.addError(new StateError("Illegal State"));
    controller.add("D");
    controller.close();
    

    View Slide

12. Stream Subscription
    var controller = new StreamController();
    controller.add("A");
    var stream = controller.stream;
    var subscription = stream.listen((str) => print(str),
    onDone : () => print("Done"));
    subscription.onError((e) {
    subscription.cancel();
    });
    controller.add("B");
    controller.add("C");
    controller.addError(new StateError("Illegal State"));
    controller.add("D");
    controller.close();
    

    View Slide

13. Stream Transformer
    var controller = new StreamController();
    var stream = controller.stream;
    var transformer = new StreamTransformer(
    handleData : (int value, EventSink sink) {
    sink.add("$value:(1)");
    sink.add("$value:(2)");
    },
    handleDone : (EventSink sink) {
    sink.add("Done!");
    }
    );
    stream.transform(transformer).forEach(print);
    for (var i = 0; i < 10; i++) {
    controller.add(i);
    }
    controller.close();
    

    View Slide

14. Stream Example
    query("input#hello").onClick.listen((MouseEvent e) {
    window.alert("hello, world.");
    });
    DOM Event
    File Access StreamSubscription> subscription;
    subscription = new File('bar.txt').openRead().listen((bytes) {
    for (var b in bytes) {
    print(new String.fromCharCode(b));
    if (b == '#'.codeUnitAt(0)) {
    subscription.cancel();
    return;
    }
    }
    });
    

    View Slide

15. Stream Example
    標準入力
    HTTP Server HttpServer.bind("127.0.0.1", 8080).then((HttpServer server) {
    server.listen((HttpRequest req) {
    req.response.write("This message from my server.");
    req.response.close();
    });
    });
    print("Please Input A.");
    var stream = stdin
    .transform(new StringDecoder())
    .transform(new LineTransformer());
    stream.listen((str){
    print("Your input's length : ${str.length}");
    print(str == "A" ? "Just A." : "Not A.");
    });
    

    View Slide