Marshalling a simple case class to/from string representation for Akka HTTP

MarshalString.scala

case class A(code:Int)

import akka.http.scaladsl.marshalling.PredefinedToEntityMarshallers._
import akka.http.scaladsl.unmarshalling.PredefinedFromEntityUnmarshallers._
  
implicit val  aResponseUnmarshaller = stringUnmarshaller.map {s:String => A(s.toInt) }
implicit val  aResponseMarshaller = StringMarshaller.compose{p:A => p.code.toString}