TypeArguments.scala

import java.lang.reflect.ParameterizedType

import com.google.common.reflect.TypeToken

import scala.reflect.ClassTag
import scala.reflect.runtime.universe._


class KV[I, O]

case class A[T] {
  val tok = new TypeToken[T](getClass) {}
}

class B[T: ClassTag] {
  val v = implicitly[ClassTag[T]]
  val clazz = implicitly[ClassTag[T]].runtimeClass
  val tok = TypeToken.of(clazz).asInstanceOf[TypeToken[T]]
}

class C[T: TypeTag] {
  val tpe = typeOf[T]
  def typeArgs(tp: Type) = tp match {
    case TypeRef(_, _, args) => args
    case _ => Nil
  }
}


object TypeTokenTest extends App {
  val a = new A[KV[Integer, String]]{}
  println(a.tok)
  println(a.tok.getType.asInstanceOf[ParameterizedType].getActualTypeArguments.toList)

  val b = new B[KV[Integer, String]]{}
  println(b.tok)  // not ok

  val c = new C[KV[Integer, String]]
  println(c.tpe.asInstanceOf[TypeRefApi].args)
  println(c.typeArgs(c.tpe))
}