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post.scala

implicit val writes: Writes[UserID] = new Writes[UserID] {
  override def writes(o: UserID): JsValue = {
    Json.toJson(o.value)
  }
}

implicit val reads: Reads[UserID] = new Reads[UserID] {
  override def reads(json: JsValue): JsResult[UserID] = {
    Reads.IntReads.reads(json).map(UserID(_))
  }
}