Tagging & Multitagging

01 tag3.scala

import scala.language.higherKinds

object tag3 {

  private def cast[T, U](v:U):T = v.asInstanceOf[T]

  type Tag[T, +U] = { type Raw = T ; type Gag <: U }
  type @@[T, +U] = T with Tag[T, U]
  type Tagged[T, +U] = T with Tag[T, U]


  trait TaggedType[T] {

    sealed trait Tag

    type Raw = T
    type Type = T @@ Tag

    def apply[K >: T](raw: K): T @@ Tag = cast(raw) //raw @@ Tag
  }




  implicit class TaggedVersion1[T](val value: T) extends AnyVal {

    def @@(typ: TaggedType[T]): T @@ typ.Tag = cast(value)

  }

  implicit class TaggedVersion2[T, U](val value: Tag[T, U]) extends AnyVal {

    def @@(typ: TaggedType[T]): T @@ (U with typ.Tag) = cast(value)

  }


  sealed trait ExceptF[F[_]]
  implicit def allowAnyF[F[_]]:ExceptF[F] = new ExceptF[F] {}
  implicit def disableComparableF:ExceptF[Comparable] = new ExceptF[Comparable] {}

  implicit class TaggedVersion3[F[_] : ExceptF, T](val value: F[T]) {
    def @@(typ: TaggedType[T]): F[T @@ typ.Tag] = cast(value)
  }

  implicit class TaggedVersion4[T, U, F[_]](val value: F[Tag[T,U]]) {
    def @@@(typ: TaggedType[T]): F[T @@ (U with typ.Tag)] = cast(value)
  }

}

02 TestTags2.scala

import tag3._

import scala.reflect.runtime.universe.reify

object TestTags2 extends App {


  System.setProperty("scala.time","true")


  object User extends TaggedType[String]
  type User = User.Type

  object User2 extends TaggedType[String]
  type User2 = User2.Type

  object User3 extends TaggedType[String]
  type User3 = User3.Type


  def checkString(user:String):Unit = {
    println(s"userString: $user, char(0)=${user.charAt(0)}")
  }
  def checkU(user:User): Unit ={
    println(s"user: ${user}, char(0)=${user.charAt(0)}")
  }
  def checkU2(user:User2): Unit ={
    println(s"user2: ${user}, char(0)=${user.charAt(0)}")
  }
  def checkU3(user:User3): Unit = {
    println(s"user3: ${user}, char(0)=${user.charAt(0)}")
  }

  val user = "Hodor" @@ User //@@@ User3
  println( reify(user))
  println(s"user0: ${user}, len: ${user.length}")



  println("--plain object.apply")
  val u0 = User("rqweq")
  checkString(u0)
  checkU(u0)

  println("--user && multi tags")
  val u1 = "Hodor" @@ User
  checkU(user)
  println(reify(u1))

  println(reify(new TaggedVersion2(u1)))

  println("---u2")

  val u2 = u1 @@ User2
  checkU(u2)
  checkU2(u2)
  println("---dddd")


  println("u2: "+u2)

  println("-----u3")
  val u3 = u2 @@ User3
  checkString(u3)
  checkU(u3)
  checkU2(u3)
  checkU3(u3)

  println("----u1+u2+u3-oneliner")
  val u4 = "Goga" @@ User @@ User2 @@ User3
  println(reify(u4))
  checkU(u3)
  checkU2(u3)
  checkU3(u3)



  println("---list")
  val rawUsers = List("scooper", "lhofstadter", "rkoothrappali")


  val users = rawUsers @@ User
  println(reify(users))
  users.foreach( checkU )

  println("---list users2")
  val users2 = new TaggedVersion4[String, User.Tag, List](users) @@@ User2
  println(reify(users2))

  users2.foreach( checkU )
  users2.foreach( checkU2 )


  //fails to refine correct type bounds for implicit class
//  println("---list[string with user.tag with user2.tag]")
//  val user3 = rawUsers @@ User @@@ User2


  println(System.currentTimeMillis())

}

03 runtime output

Expr[io.treeve.tag3.@@[java.lang.String,io.treeve.TestTags2.User.Tag]](TestTags2.this.user)
user0: Hodor, len: 5
--plain object.apply
userString: rqweq, char(0)=r
user: rqweq, char(0)=r
--user && multi tags
user: Hodor, char(0)=H
Expr[io.treeve.tag3.@@[java.lang.String,io.treeve.TestTags2.User.Tag]](TestTags2.this.u1)
Expr[io.treeve.tag3.TaggedVersion2[io.treeve.TestTags2.u1.Raw,io.treeve.TestTags2.u1.Gag]](new tag3.TaggedVersion2(TestTags2.this.u1))
---u2
user: Hodor, char(0)=H
user2: Hodor, char(0)=H
---dddd
u2: Hodor
-----u3
userString: Hodor, char(0)=H
user: Hodor, char(0)=H
user2: Hodor, char(0)=H
user3: Hodor, char(0)=H
----u1+u2+u3-oneliner
Expr[io.treeve.tag3.@@[<refinement>.this.Raw,<refinement>.this.Gag with io.treeve.TestTags2.User3.Tag]](TestTags2.this.u4)
user: Hodor, char(0)=H
user2: Hodor, char(0)=H
user3: Hodor, char(0)=H
---list
Expr[List[io.treeve.tag3.@@[java.lang.String,io.treeve.TestTags2.User.Tag]]](TestTags2.this.users)
user: scooper, char(0)=s
user: lhofstadter, char(0)=l
user: rkoothrappali, char(0)=r
---list users2
Expr[scala.List[io.treeve.tag3.@@[String,io.treeve.TestTags2.User.Tag with io.treeve.TestTags2.User2.Tag]]](TestTags2.this.users2)
user: scooper, char(0)=s
user: lhofstadter, char(0)=l
user: rkoothrappali, char(0)=r
user2: scooper, char(0)=s
user2: lhofstadter, char(0)=l
user2: rkoothrappali, char(0)=r
1495609044246
[total 50ms]
[success] Total time: 2 s, completed 24.05.2017 9:57:24