problem.scala

object Example {

  def failsHorribly[T1 <: Tuple, T2 <: Tuple](f: () => Either[Unit, Tuple.Concat[T1, T2]])(using size: Tuple.Size[T1]): () => Either[Unit, T2] = {
    () => {
      f() match {
        case Left(_) => Left(())
        case Right(item) => Right(item.drop(size).asInstanceOf[T2])
      }
    }
  }

}