shapeless_tags_fun.scala

shapeless_tags_fun.scala

object UserRelationsT {
  import shapeless.tag
  import tag.@@
  import cats.data.Ior

  trait IsFollowerTag
  type IsFollower = Boolean @@ IsFollowerTag
  def isFollower(b: Boolean): IsFollower = tag[IsFollowerTag][Boolean](b)

  trait IsFollowingTag
  type IsFollowing = Boolean @@ IsFollowingTag
  def isFollowing(b: Boolean): IsFollowing = tag[IsFollowingTag][Boolean](b)

  type Rel = Ior[IsFollowing, IsFollower]

  implicit class OptionTagOps[U, I](opt: Option[U @@ I]) {
    def getOrElseT[B >: U](default: B): @@[B, I] = {
      opt.getOrElse(tag[I][B](default))
    }
  }

  val example1 = Ior.left(isFollower(true)).left.getOrElseT(false) //works fine
  val casted1: IsFollower = example1 //works fine
  val example2: IsFollower = Ior.left(isFollower(true)).left.getOrElseT(false) //compilation error

  /*
    md70.sc:1: type mismatch;
     found   : Boolean(false)
     required: shapeless.tag.Tagged[$sess.cmd62.IsFollowerTag] with Boolean
    val example2: IsFollower = Ior.left(isFollower(true)).left.getOrElseT(false)
                                                                          ^
   */
}

What I want here is such getOrElse that is able to wrap result in expected @@