pub type MapAndDrop<S, T, P, F, U> = AndThen<Either<FutureResult<(S, Vec<U>), Error>, Map<T, P, F, U>>, (BoxFuture<T>, FutureResult<Vec<U>, Error>), fn(_: (S, Vec<U>)) -> (BoxFuture<T>, FutureResult<Vec<U>, Error>)>;