Distinct() 在 Stream 上使用时似乎不会过滤掉相同的结果

Posted 2023-02-23

【中文标题】Distinct() 在 Stream 上使用时似乎不会过滤掉相同的结果

【英文标题】：Distinct() doesn't seem to filter out identical results when used on a Stream

【发布时间】：2020-12-13 05:17:31

【问题描述】：

请看一下这段代码 =>

void main() async 
  Stream<int> _intStream() async* 
    for (int i = 0; i < 10; i++) yield i;
  

  Stream<int> _even() => _intStream().where((int i) => i % 2 == 0);
  Stream<bool> _isEven(Stream<int> stream) => stream.map((int i) => i % 2 == 0);

  print('test 1: should print 5 [true] and 5 [false] alternate');
  await for (bool b in _isEven(_intStream())) 
    print('test 1: $b');
  

  print('test 2: should print 5 [true]');
  await for (bool b in _isEven(_even())) 
    print('test 2: $b');
  

  print('test 3: should print ONLY ONE [true]');
  await for (bool b in _isEven(_even().distinct())) 
    print('test 3: $b');
  

我是不是用错了distinct()？

提前谢谢你

【参考方案1】：

没关系，我只是把 distinct 放在错误的地方， 以下按预期工作

void main() async 
  Stream<int> _intStream() async* 
    for (int i = 0; i < 10; i++) yield i;
  

  Stream<int> _even() => _intStream().where((int i) => i % 2 == 0);
  Stream<bool> _isEven(Stream<int> stream) => stream.map((int i) => i % 2 == 0);

  print('test 1: should print 5 [true] and 5 [false] alternate');
  await for (bool b in _isEven(_intStream())) 
    print('test 1: $b');
  

  print('test 2: should print 5 [true]');
  await for (bool b in _isEven(_even())) 
    print('test 2: $b');
  

  print('test 3: should print ONLY ONE [true]');
  await for (bool b in _isEven(_even()).distinct()) 
    print('test 3: $b');