object FunctionToFlow {

  import akka.stream._
  import akka.stream.scaladsl.{ FlowGraph, Flow }

  def apply[A, B](f: A => B): Graph[FlowShape[A, B], Unit] =
    FlowGraph.partial() { implicit b =>
      val transformation = b.add(Flow[A].map(f))
      new FlowShape[A, B](
        transformation.inlet,
        transformation.outlet
      )
    }
}