I think toArray[Any] will box the values. So that could be improved. Otherwise, however, looks great!

It will box the values but Java doesn't provide an implementation of sorting an array that accepts an arbitrary comparison function and doesn't box values. I don't think we can do better in the general case without doing our own implementation of sorting algorithms, which doesn't seem like the greatest, but we could match on the Ordering and use the specialized sorted on primitive arrays if it is the default ordering.