Consider pre-packaging the "PreMaterialize" pattern (we could late optimize it too) #23895
Description
Pretty sure not many people can ad-hoc whip up this pattern to get a materialized value powered source to emit an entity yet it's very useful in practice:
example:
val introspector = path("introspector") {
concat(
path(Segment / "inspect") { id ⇒
val refSource = Source.actorRef[ReplicatedIntrospector.Event](Int.MaxValue, OverflowStrategy.fail)
.map(_.render)
// TODO "pre-materialize pattern"
val (ref, pub) =refSource.toMat(Sink.asPublisher(true))(Keep.both).run()
val s = Source.fromPublisher(pub)
.intersperse("\n")
.map(ByteString(_))
// end of "pre-materialize pattern"
introspectorProxy.tell(ReplicatedIntrospector.Inspect, ref)
complete(HttpResponse(entity = HttpEntity(ContentTypes.`text/plain(UTF-8)`, s)))
}
)
}
I think we should be able to pre-build such a thing perhaps, document it as pre-materialize something and allow users to use it thanks to that rather than have them re-invent this pattern