It's probably a bit much for your book, but this operation can be written without any state or pesky strongifying:

```objc
RAC(self, loading) = [[[RACObserve(self, model)
    sample:self.didBecomeActiveSignal]
    map:^(FRPPhotoModel *model) {
        return [[[[[FRPPhotoImporter
            fetchPhotoDetails:model]
            catch:^(NSError *error) {
                NSLog(@"Could not fetch photo details: %@", error);
                return [RACSignal empty];
            }]
            doCompleted:^{
                NSLog(@"Fetched photo details.");
            }]
            startWith:@NO]
            concat:[RACSignal return:@YES]];
    }]
    concat];
```