gistfile1.scala

Welcome to Scala version 2.9.1.final (Java HotSpot(TM) Server VM, Java 1.6.0_18).
Type in expressions to have them evaluated.
Type :help for more information.

scala> type Tagged[U] = { type Tag = U }
defined type alias Tagged

scala> type @@[T, U] = T with Tagged[U]
defined type alias $at$at


scala> object O {
     | def tag[T] = new { def apply[@specialized(scala.Int, scala.Long) U](u: U): U with Tagged[T] = u.asInstanceOf[U @@ T] }
     | }
defined module O

scala> :javap O
Compiled from "<console>"
public final class O$ extends java.lang.Object implements scala.ScalaObject{
    public static final O$ MODULE$;
    public static {};
    public java.lang.Object tag();
    public O$();
}

//BELOW WORKS BETTER
scala> object O {
     | def tag[T, @specialized(scala.Int, scala.Long) U](u: U): U with Tagged[T] = u.asInstanceOf[U @@ T]
     | }
defined module O

scala> :javap O
Compiled from "<console>"
public final class O$ extends java.lang.Object implements scala.ScalaObject{
    public static final O$ MODULE$;
    public static {};
    public java.lang.Object tag(java.lang.Object);
    public int tag$mIc$sp(int);
    public long tag$mJc$sp(long);
    public O$();
}