Future/Stream/async-await

Dart 的异步基于 Future（一次性）与 Stream（多次）。

Future 与 async/await

Future<int> fetch() async {
  await Future.delayed(Duration(milliseconds: 100));
  return 42;
}

Stream

Stream<int> gen() async* {
  for (var i = 0; i < 3; i++) {
    yield i;
  }
}

void main() async {
  await for (final v in gen()) {
    print(v);
  }
}

错误处理与超时

final v = await fetch().timeout(const Duration(seconds: 2), onTimeout: () => -1);
try {
  final x = await fetch();
} catch (e, st) {
  // 统一记录或重试
}

组合并发

final results = await Future.wait<int>([
  fetch(),
  fetch(),
], eagerError: true);

StreamController 与广播

final ctrl = StreamController<int>.broadcast();
final sub = ctrl.stream.listen((v) {});
ctrl.add(1);
await sub.cancel();
await ctrl.close();