Future & Stream in Dart

Transcript

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   Future & Stream in Dart tomochikahara @zetta1985

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   Agenda • Future API • Stream API

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   Future API for Ansynchronous Programming

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   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
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   Future & Completer Completer Future Future Caller Callee Future<String> echoToMountain(String

   yo_ho); call echoToMountain create get Future return Future then((reply) => catchMyEar(reply)) complete(reply) Execution
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   Future & Completer import "dart:async"; Future<String> echoToMountain(String yo_ho) { var

   completer = new Completer<String>(); 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"); }
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   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); });
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   Stream API for sequence of any data

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   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
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    Stream What is a Stream? Controller (Sink) Subscription D C

    B' A' ・・・ Transformer F E add listen
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    Stream var controller = new StreamController<String>(); 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();
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    Stream Subscription var controller = new StreamController<String>(); 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();
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    Stream Transformer var controller = new StreamController<int>(); var stream =

    controller.stream; var transformer = new StreamTransformer<int, String>( handleData : (int value, EventSink<String> sink) { sink.add("$value:(1)"); sink.add("$value:(2)"); }, handleDone : (EventSink<String> sink) { sink.add("Done!"); } ); stream.transform(transformer).forEach(print); for (var i = 0; i < 10; i++) { controller.add(i); } controller.close();
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    Stream Example query("input#hello").onClick.listen((MouseEvent e) { window.alert("hello, world."); }); DOM Event

    File Access StreamSubscription<List<int>> 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; } } });
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    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."); });