Play JSON formatter generater for NewType wrapper types

NewTypeJsonFormats.scala

import play.api.libs.json._


object NewTypeJsonFormats {

  /**
    * Returns a Json Formatter for newtype wrappers
    *
    * Adapted from https://groups.google.com/d/msg/play-framework/zDUxEpEOZ6U/-7BpwI8iBCoJ
    * Usage: NewTypeJsonFormats(UserId.apply)(UserId.unapply)
    */
  def apply[I: Format, T](f1: I => T)(f2: T => Option[I]) = new Format[T] {
    def reads(js: JsValue): JsResult[T] = js.validate[I] map f1
    def writes(id: T): JsValue = Json.toJson(f2(id))
  }

}