RAC的高阶操作：repeat、flatten组合

改变某个值的个数：

RACSignal *signalA = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
  [subscriber sendNext:@1];
  [subscriber sendNext:@2];
  [subscriber sendNext:@3];
  [subscriber sendNext:@4];
  [subscriber sendNext:@5];
  [subscriber sendCompleted];
  return [RACDisposable disposableWithBlock:^{
    NSLog(@"signalA1完成");
  }];
}];
    
RACSignal *signalB = [[signalA map:^id(NSNumber *value) {
  return [[[RACSignal return:value] repeat] take:value.integerValue];
}] flatten];

[signalB subscribeNext:^(RACSignal *x) {
  NSLog(@"subscribeNext:%@",x);
}];

2021-04-15 16:18:15.494267+0800 XXXXXX[3806:1098169] subscribeNext:1

2021-04-15 16:18:15.495839+0800 XXXXXX[3806:1098169] subscribeNext:2

2021-04-15 16:18:15.495970+0800 XXXXXX[3806:1098169] subscribeNext:3

2021-04-15 16:18:15.496114+0800 XXXXXX[3806:1098169] subscribeNext:4

2021-04-15 16:18:15.496359+0800 XXXXXX[3806:1098169] subscribeNext:5

2021-04-15 16:18:15.497260+0800 XXXXXX[3806:1098169] signalA1完成

2021-04-15 16:18:24.786032+0800 XXXXXX[3806:1098169] subscribeNext:2

2021-04-15 16:18:24.787346+0800 XXXXXX[3806:1098169] subscribeNext:3

2021-04-15 16:18:24.787594+0800 XXXXXX[3806:1098169] subscribeNext:4

2021-04-15 16:18:24.788007+0800 XXXXXX[3806:1098169] subscribeNext:5

2021-04-15 16:18:24.788239+0800 XXXXXX[3806:1098169] subscribeNext:3

2021-04-15 16:18:24.788723+0800 XXXXXX[3806:1098169] subscribeNext:4

2021-04-15 16:18:24.789010+0800 XXXXXX[3806:1098169] subscribeNext:5

2021-04-15 16:18:24.789369+0800 XXXXXX[3806:1098169] subscribeNext:4

2021-04-15 16:18:24.789648+0800 XXXXXX[3806:1098169] subscribeNext:5

2021-04-15 16:18:24.789986+0800 XXXXXX[3806:1098169] subscribeNext:5