Too much cake!

example.scala

trait Registry {
  val ec:ExecutionContext
  val userService = new UserServiceImpl(ec)
  val fooBarService = new FoobarServiceImpl(userService)
}

class RestActor extends Registry with UserRoutes {
  def receive = {
    userRoutes ~
    otherRoutesFromOtherMixins
  }
}

trait AccessDirectives extends Directives {
  self: Registry =>
  
  val letMeIn:Directive1[Option[User]] = optionalHeaderValueByName("user_auth").hflatMap {
    case Some(id) :: HNil => onSuccess(userService.get(id))
    case _ => reject()
  }
}

trait UserRoutes extends AccessDirectives with HttpService {
  self: Registry =>
  
  val userRoutes = {
    path(Segment){ userId =>
      onSuccess(userService.get(userId)){ user =>
        complete(user)
      }
    }
  }
}