Does this actually have a retain cycle?

blockretain.m

#import <Foundation/Foundation.h>

@interface A : NSObject
- (void)doThingWithObject:(id)o completion:(void(^)(void))completionHandler;
@end

@implementation A
- (void)doThingWithObject:(id)o completion:(void(^)(void))completionHandler
{
	NSLog(@"object: %@", o);
	dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        if(completionHandler) completionHandler();
    });
}
@end

int main(int argc, char *argv[]) {
  @autoreleasepool {
    A *a = [A new];
    NSArray *someThings = @[@0, @1, @2];
    NSEnumerator *e = [someThings objectEnumerator];
    __block void(^ completionHandler)(void);
    completionHandler = ^{
      id o = [e nextObject];
      if (o) {
        [a doThingWithObject:o completion:completionHandler];
      }
    };
    completionHandler = [completionHandler copy];
    completionHandler();
    sleep(1);
  }
}

See https://gist.github.com/iamleeg/7911205 which no longer has the warning. I think it doesn't have a retain cycle either, but now I'm unsure. :-S

There's no leak, but only because we know that nextObject will at some point return nil. The compiler doesn't know that, so it warns. I guess even if nextObject never returned nil there wouldn't be a "leak" because the block would continually be doing something. It depends on your definition of leak really :-).

To me, this kind of logic is a smell anyway and the warning is useful.