ReactiveCocoaでKVOの新旧の値を受け取る

gistfile1.txt

[[object rac_valuesAndChangesForKeyPath:@keypath(object, keypath) options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld observer:nil] subscribeNext:^(RACTuple *tuple) {
    NSDictionary *changeDictionary = tuple.second;
    if (![changeDictionary[@"new"] isEqualToNumber:changeDictionary[@"old"]]) {
    }
}];