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objective-cios7reactive-cocoa

ReactiveCocoa. Return type 'UIImage *' must match previous return type 'void *'

@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@property (nonatomic) UIImage *image;
@property (nonatomic) PhotoEffect *effect;
@property (weak, nonatomic) IBOutlet UISwitch *glossSwitch;

I'm trying to update imageView with a modified image, when UISwitch changed its value, or _image and _effect were changed. 

RAC(self.imageView, image) = [RACSignal
                                  combineLatest:@[ RACObserve(self, image), RACObserve(self.glossSwitch, on), RACObserve(self, effect)]
                                  reduce:^(UIImage *im, NSNumber *gloss, PhotoEffect *effect) {
                                      if (!im) {
                                          return nil;
                                      }
                                      if (effect) {
                                          im = [im imageWithEffect:effect.type];
                                      }
                                      if (gloss.boolValue) {
                                          im = [GlossyIcon applyShineToImage:im];
                                      }
                                      return im;
                                  }];

This code gives a compiler error, which I can't understand:

Return type 'UIImage *' must match previous return type 'void *' 
when block literal has unspecified explicit return type
Solution

  • Since your reduce block can return nil or UIImage *, the compiler can't infer the return type of the block. Explicitly declaring a return type for the reduce block will fix the problem, you can use id for brevity, or UIImage * to be clear.

        reduce:^UIImage * (UIImage *im, …) {