Dart17.递归生成器

yield* 以指针的方式传递递归对象，而不是整个同步对象。

ex:

void main(){
  //递归生成器
  //同步
  var it1 = getSyncRecursiveGenerator(5).iterator;
  while (it1.moveNext()) {
    print(it1.current);
  }
  print('========================================');
  //异步
  getAsyncRecursiveGenerator(5).listen((value) => print(value));
  print('over');
}

//递归生成器：使用yield*
Iterable getSyncRecursiveGenerator(int n) sync* {
  if (n > 0) {
    yield n;
    yield* getSyncRecursiveGenerator(n - 1);
  }
}

//异步递归生成器
Stream getAsyncRecursiveGenerator(int n) async* {
  if (n > 0) {
    yield n;
    yield* getAsyncRecursiveGenerator(n - 1);
  }
}

输出：

D:\flutter\bin\cache\dart-sdk\bin\dart.exe --enable-asserts --enable-vm-service:48558 D:\Code\Flutter\FlutterHello\flutter_app\lib\tree.dart
Observatory listening on http://127.0.0.1:48558/9zihU-Lbn9E=/

lib/tree.dart: Warning: Interpreting this as package URI, 'package:flutterapp/tree.dart'.
5
4
3
2
1
========================================
over
5
4
3
2
1

Process finished with exit code 0