Objective-C block的参数问题: This block declaration not a prototype

Question

我在学 ReactiveObjC, ReactiveCocoa的Objective-C版.
RACSignal.h 中，以下代码:,

- (RACSignal *)reduceEach:(id _Nullable (^)())reduceBlock
RAC_WARN_UNUSED_RESULT; (id _Nullable (^)())

Xcode 报错:

This block declaration is not a prototype

reduceBlock()能放很多参数.
UIAlertView+RACSignalSupport.m 中，以下代码， 其他文件也有 ,

- (RACSignal *)rac_buttonClickedSignal {

RACSignal *signal = [[[[self.rac_delegateProxy
    signalForSelector:@selector(alertView:clickedButtonAtIndex:)]
    reduceEach:^(UIAlertView *alertView, NSNumber *buttonIndex){
        return buttonIndex;
    }]
......
return signal; }

有点泛型的感觉。
void (^block)() 这样声明，就能在block 放0到多个参数了.
Xcode现在不支持这种语法，怎样解决，解释下更好。

Answer 1

只是个warnning吧，

试试 括号里面加上

id _Nullable ,...

//比如

@property (nonatomic, strong) void (^testBlock)(id _Nullable ,...);