Bottom.scala

import scala.reflect.ClassTag

object Bottom extends App {

  class C[T](implicit ev: reflect.ClassTag[T]) {
    def ct: reflect.ClassTag[T] = ev
  }
  class X[U, -T]

  object X {
    implicit def genericX[U, T <: U](implicit ev: T <:< U): X[U, T] = new X[U, T]
  }

  type Bottom <: Nothing

  implicit val bottomClassTag: ClassTag[Bottom] = implicitly[ClassTag[Nothing]]

  implicitly[X[AnyRef, AnyRef] <:< X[AnyRef, Bottom]] // compiles
  implicitly[X[String, Bottom]] // compiles


  def check[T >: Bottom <: AnyRef](implicit ev: X[AnyRef, T], ct: ClassTag[T]): C[T] = new C

  println(check.ct) // compiler infers T == Nothing, (and not T == AnyRef), despite contravariant T
  println(check[String].ct)
}