welf

welf.m

@interface AsyncAPI : NSObject 
- (void)doSomethingForOwner:(__weak id)owner completionBlock:(void (^)(id welf, id result))complete;
@end

@implementation AsyncAPI
- (void)doSomethingForOwner:(__weak id)owner completionBlock:(void (^)(id welf, id result))complete {
    [self doTheAsyncThing:^(id result) {
        if (owner && complete) {
            complete(owner, result);
        }
    }];
}
- (void)doTheAsyncThing:(void (^)(id result))complete {
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        complete(@42);
    });
}
@end

@interface MyClass : NSObject
- (void)frob;
@end

@implementation MyClass
- (void)frob {
    AsyncAPI *api = [AsyncAPI new];
    [api doSomethingForOwner:self completionBlock:^(id welf, id result) {
        [welf whatever];
    }];
}
- (void)whatever {}
@end