Dart 同步、异步

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sync* 同步

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main() {
  print('==== start ====');

  getList(10).forEach(print);

  print('==== end ====');
}

Iterable<int> getList(int count) sync* {
  for (int i = 0; i < count; i++) {
    yield i;
  }
}

执行结果：

sync 调用 sync

注意 yield* 的使用

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main() {
  print('==== start ====');

  getList(10).forEach(print);

  print('==== end ====');
}


Iterable<int> getList(int count) sync* {
  yield* generate(count);
}

Iterable<int> generate(int count) sync* {
  for (int i = 0; i < count; i++) {
    yield i;
  }
}

执行结果：

async 异步

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main() {
  print('==== start ====');

  getList(5).then(print);

  print('==== end ====');
}

Future<int> getList(int count) async {
  await sleep();
  for (int i = 0; i < count; i++) {
    print('for $i');
  }
  return 99;
}

/// 延迟3秒
Future sleep() async {
  return Future.delayed(Duration(seconds: 3));
}

执行结果：

async* + Stream

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main() {
  print('==== start ====');

  getList(5).listen(print);

  print('==== end ====');
}

Stream<int> getList(int count) async* {
  for (int i = 0; i < count; i++) {
    await Future.delayed(Duration(seconds: 1));

    yield i;
  }
}

执行结果：

async* 调用 async*

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main() {
  print('==== start ====');

  getList(5).listen(print);

  print('==== end ====');
}

Stream<int> getList(int count) async* {
  yield* generate(count);
}

Stream<int> generate(int count) async* {
  for (int i = 0; i < count; i++) {
    await Future.delayed(Duration(seconds: 1));
    yield i;
  }
}

执行结果：