trying to pass along the type of a PathMatcher to a abstract Route member

ApiFormats.scala

package gist.chadselph

import akka.http.scaladsl.server.PathMatcher
import akka.http.scaladsl.server._
import akka.http.scaladsl.server.Directives._
import akka.http.scaladsl.server.util.ApplyConverter

/**
  * Created by chad on 11/4/16.
  */
abstract class ApiFormats[PathType](val basePath: PathMatcher[PathType],
                                    // include as parameter, because implicits are private, so
                                    // their type members can't be exported
                                    val hac: ApplyConverter[PathType]) {

  def create: hac.In

  final val createRoute: Route = {
    val matcher = post & path(basePath)
    matcher.tapply(hac(create))
  }


}

object Foo {

  val v1Formats = new ApiFormats("v1" / Segment / "things" / Segment,
    implicitly[ApplyConverter[(String, String)]]) {

    /*
    Information:scalac: => (String, String) => akka.http.scaladsl.server.Route <: => this.hac.In?
    Information:scalac: false

    Error:(31, 18) overriding method create in class ApiFormats of type => this.hac.In;
     value create has incompatible type
     */
    override val create: ((String, String) => Route) = { (f, s) =>
      complete(f)
    }
  }

}