Transforming a Future of HttpResponse to a Future of a case class using generics through json4s

transformHttpResponse.scala

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._
import akka.stream.Materializer
import akka.util.ByteString
import org.json4s._
import org.json4s.native.JsonMethods._

import scala.concurrent.duration._
import scala.concurrent.{ExecutionContext, Future}


class HttpClient(implicit system: ActorSystem,
                materializer: Materializer,
                ec: ExecutionContext) {
  implicit val formats: Formats = DefaultFormats
  private def transformResponse[T](r: Future[HttpResponse])
                                  (implicit ev: scala.reflect.Manifest[T]): Future[T] = {
    r.flatMap {
      case response@HttpResponse(StatusCodes.OK, _, _, _) => {
        val buffer = ByteString("")

        response.entity.dataBytes
          .runFold(buffer)(_ ++ _)
          .map(_.utf8String)
          .map(parse(_).extract[T])
      }
      case _: Any => throw new Throwable("Error!")
    }
  }
}