Not Supported breakOut rewrite

[MasseGuillaume]

https://github.com/akka/akka/blob/d76b27ba3ecf747743d1fc6abd3163f78c9c60d8/akka-persistence/src/main/scala/akka/persistence/snapshot/local/LocalSnapshotStore.scala#L76-L81

  override def deleteAsync(persistenceId: String, criteria: SnapshotSelectionCriteria): Future[Unit] = {
    val metadatas = snapshotMetadatas(persistenceId, criteria)
    Future.sequence {
      metadatas.map(deleteAsync)
    }(collection.breakOut, streamDispatcher).map(_ ⇒ ())(streamDispatcher)
  }

[MasseGuillaume]

This breakOut is a no-op:

def sequence[A, M[X] <: TraversableOnce[X]](in: M[Future[A]])(implicit cbf: CanBuildFrom[M[Future[A]], A, M[A]], executor: ExecutionContext): Future[M[A]]
def traverse[A, B, M[X] <: TraversableOnce[X]](in: M[A])(fn: (A) ⇒ Future[B])(implicit cbf: CanBuildFrom[M[A], B, M[B]], executor: ExecutionContext): Future[M[B]]

The M does not change. It's only a default parameter to set an ExecutionContext

For example, this does not compile:

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
Future.sequence(List(Future(1)))(breakOut, global): Future[Vector[Int]]
Future.traverse(List(1))(x => Future(x))(breakOut, global): Future[Vector[Int]]
// type mismatch;
// found   : scala.concurrent.Future[List[Int]]
// required: scala.concurrent.Future[Vector[Int]]
//  Future.sequence(List(Future(1)))(breakOut, global): Future[Vector[Int]]
//                 ^
// type mismatch;
// found   : scala.concurrent.Future[List[Int]]
// required: scala.concurrent.Future[Vector[Int]]
//  Future.traverse(List(1))(x => Future(x))(breakOut, global): Future[Vector[Int]]
//                 ^

It's possible to change the collection type:

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
Future.sequence(List(Future(1)))(breakOut, global): Future[Seq[Int]]
Future.traverse(List(1))(x => Future(x))(breakOut, global): Future[Seq[Int]]