tagging value classes does not work

[kwark]

Hello,

This tagging library is suffering from the same issue as shapeless: milessabin/shapeless#644

object Main extends App {

  trait FooTag
  case class A(value: Int) extends AnyVal

  import com.softwaremill.tagging._

  val foo = A(0).taggedWith[FooTag]

  println(Array(foo).apply(0))
  println(List(foo).head)

}

This will throw a ClassCastException

You can also run/checkout this scastie: https://scastie.scala-lang.org/kwark/h4No8bhdQGKIEBV14rTkrA

A solution is to make Tag a universal trait instead of a type alias:

trait Tag[+U] extends Any { type Tag <: U }

Also see: https://scastie.scala-lang.org/kwark/575syCWTQIWsVaeJAKVxoQ

You might want to check binary compatibility.

[kciesielski]

Sorry for long silence, thanks a lot for reporting the issue and proposing a solution. As far as I checked it works well and there are no issues with binary compatibility. I'm preparing a proper fix.