Acked replicateN

AckedReplicate.scala

import scala.concurrent.{ExecutionContext, Future, Promise}
import cats.instances.future._
import cats.syntax.functor._
import com.timcharper.acked.AckTup
import shapeless.{Nat, Sized}
import shapeless.syntax.sized._
import shapeless.ops.nat.ToInt

object AckedReplicate {
  def replicateN[T, N <: Nat](implicit size: ToInt[N]): AckTup[T] => Sized[List[AckTup[T]], N] = {
    at: AckTup[T] =>
      implicit val ec: ExecutionContext = SameThreadExecutionContext

      val (p, t) = at

      val promises: List[Promise[Unit]] = List.fill(size())(Promise[Unit])
      val sizedPs: Sized[List[Promise[Unit]], N] = promises.sized[N].get // I know what I do, scalac
      val futures = promises.map(_.future)

      Future.sequence(futures).void.onComplete(p.tryComplete)

      sizedPs.map(_ -> t)
  }
}

usage.scala

import shapeless.nat.{_2, _3, _4, _6}

val bc = builder.add(UnzipWith(AckedReplicate.replicateN[XXX, _6].andThen(_.tupled)))