> If you change your internal software structure and the data is stored in another way or you choose the make your library concurrent internally where differen

> If you change your internal software structure and the data is stored in another way or you choose the make your library concurrent internally where different parts could mutate the vector while the user might request the same data in parallel then returning the slice would no longer be possible In that case you wouldn't want to return a slice, because it would be dangerous. The compiler would prevent you from invalidating an API use case. I don't see a problem here.