package test.sixtysevenninetyone

object UCs {
  abstract class Ooh[+A] extends Tuple1[Unit](()) {
    val phantom: A
  }
  def ooh[A](a: => A): Ooh[A] = new Ooh[A]{lazy val phantom = a}

  def uc1[A, B]: A =:= B = {
    val aa = ooh(implicitly[A =:= A])
    val no = ooh(???)
    aa match {case ano: no.type => ano.phantom}
  }

  import collection.mutable.Buffer

  def uc2[A, B]: A =:= B = {
    val es = Buffer[A =:= B]()
    val gs = Buffer[A =:= A]()
    (gs: Buffer[_]) match {
      case es: es.type => gs += implicitly; es.head
    }
  }

  def oops = (uc1[String, ClassLoader]("twenty-one"),
              uc2[String, ClassLoader]("forty-two"))
}

[warn] 6791.scala:12: non-variable type argument Nothing in type pattern test.sixtysevenninetyone.UCs.Ooh[Nothing] is unchecked since it is eliminated by erasure
[warn]     aa match {case ano: no.type => ano.phantom}
[warn]                           ^
[warn] 6791.scala:21: non-variable type argument =:=[A,B] in type pattern scala.collection.mutable.Buffer[=:=[A,B]] is unchecked since it is eliminated by erasure
[warn]       case es: es.type => gs += implicitly; es.head
[warn]                  ^
[warn] four warnings found
[info] Starting scala interpreter...
[info] 
Welcome to Scala version 2.11.0-M7 (OpenJDK 64-Bit Server VM, Java 1.7.0_45).
Type in expressions to have them evaluated.
Type :help for more information.

scala> test.sixtysevenninetyone.UCs.oops
res0: (ClassLoader, ClassLoader) = (twenty-one,forty-two)