Simple, Static Scala dependency injection with Shapeless

DependencyInjection.scala

package test_shapeless

object DI {
  import shapeless._

  trait Injecter[L <: HList, A] {
    def apply(l: L) : A
  }

  trait InjecterAux[L <: HList, A] {
    def apply(l: L) : A
  }

  object Injecter {
    implicit def injecter[L <: HList, A0](implicit injecter: InjecterAux[L, A0]) = new Injecter[L,A0] {
      def apply(l:L) : A0 = injecter(l)
    }
  }

  object InjecterAux {
    implicit def foo[L <: HList, A, Out0 <: HList]
        (implicit subtypeUnifier: SubtypeUnifierAux[L, A, Out0], filter: FilterAux[Out0, A, A :: HNil]) =
          new InjecterAux[L,A] {

      def apply(l:L) : A = filter(subtypeUnifier(l)).head
    }
  }

  implicit class Injector[L <: HList](l:L) {
    def inject[A](implicit injecter: Injecter[L,A]) : A = injecter(l)
  }
}

object DependencyInjectionTest extends App {

  import shapeless._


  trait ServiceOneImpl { def hello : String }
  class ServiceOneImpl_0 extends ServiceOneImpl { val hello = "impl_0" }

  trait ServiceMultiImpl { def hello: String }
  class ServiceMultiImpl_1 extends ServiceMultiImpl { val hello = "impl_1"}
  class ServiceMultiImpl_2 extends ServiceMultiImpl { val hello = "impl_2"}


  trait Marker

  val register =
    (new ServiceOneImpl_0) ::
    (new ServiceMultiImpl_1) ::
    (new ServiceMultiImpl_2 with Marker) ::
    HNil


  implicit class Uniqueable[L <: HList](l: L) {
    def unique[A](implicit filter: FilterAux[L, A, A :: HNil]) = {
      filter(l).head
    }
  }

  //implementation work
  val s1 = register.unique[ServiceOneImpl_0]
  println(s1.hello) //impl_0

  val s2 = register.unifySubtypes[ServiceOneImpl].unique[ServiceOneImpl]
  println(s2.hello) //impl_0

  val s3 = register.unifySubtypes[ServiceMultiImpl with Marker].unique[ServiceMultiImpl with Marker]
  println(s3.hello) //impl_2


  import DI._

  val s4 = register.inject[ServiceOneImpl_0]
  println(s4.hello) //impl_0

  val s5 = register.inject[ServiceOneImpl]
  println(s5.hello) //impl_0

  val s6 = register.inject[ServiceMultiImpl with Marker]
  println(s6.hello) //impl_2
}