@johnynek so it make sense to add ``` def appendAll(old: B, items: TraversableOnce[A]): B ``` to the base trait but can we also have specialized ``` def appendAll(items: TraversableOnce[A]): B ``` in MonoidAggregator and RingAggregator? TBH in case of both MonoidAggregator and RingAggregator ```old:B`` will be monoid.zero or ring.one respectively, so why not abstract that from the user. As a client I expect the library to take care of that if I am already providing monoid or ring. Let me know if it make sense