Desugaring TypeTag's in Scala

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Joe San

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Jan 22, 2018, 10:59:13 AM1/22/18

to scala-user

I have the following code snippet:

import scala.reflect.runtime.universe._

def paramInfo[N: TypeTag](x: N): Unit = {
  val targs = typeOf[N] match { case TypeRef(_, _, args) => args }
  println(s"type of $x has type arguments $targs")
}

case class Dummy(l: List[Int])

import scala.reflect.runtime.universe._
paramInfo: [N](x: N)(implicit evidence$1: reflect.runtime.universe.TypeTag[N])Unit
defined class Dummy

// Exiting paste mode, now interpreting.

type of Dummy(List(1, 2)) has type arguments List()

scala> paramInfo(List(1,2))
type of List(1, 2) has type arguments List(Int)

scala> paramInfo(Dummy(List(1,2)))
type of Dummy(List(1, 2)) has type arguments List()

What I do not understand is that I was expecting the call paramInfo(Dummy(List(1,2))) to actually print:

type of Dummy(List(1, 2)) has type arguments List(Dummy(List(Int)))