Well typed REST skeleton

TypedRest.scala

object TypedRest {
  type Id[A] = Long

  object Request {
    private[this] trait HasId[A] {
      val id: Id[A]
    }
    trait Get[A] extends HasId[A]
    trait Put[A] extends HasId[A]
    trait Post[A]
    trait Patch[A] extends HasId[A]
    trait Delete[A] extends HasId[A]
  }

  import Request._

  trait Repo[A] {
    def apply(): Iterable[Get[A]]
    def apply(id: Id[A]): Get[A]
    def +=(request: Post[A]): Get[A]
    def update(request: Put[A]): Get[A]
    def update(request: Patch[A]): Get[A]
    def -=(request: Delete[A]): Get[A]
  }
  
  abstract class CachedRepo[A](cache: Cache[A], repo: Repo[A]) extends Repo[A] {
    private[this] def apply(value: Get[A]): Get[A] = {
      cache(value.id) = value
      value
    }
    override def apply() = cache.values
    override def apply(id: Id[A]) = cache(id)
    override def +=(request: Post[A]) = apply(repo += request)
    override def update(request: Put[A]) = apply(repo.update(request))
    def update(request: Patch[A]) = apply(repo.update(request))
    def -=(request: Delete[A]) = {
      val result = repo -= request
      cache.remove(result.id)
      result
    }
  }
  
  type Cache[A] = Map[Id[A], Get[A]]
}