Hacking generalized type constraints.

execution.txt

> scalac GenTypeConstraints.scala
> scala GenTypeConstraints 
2
FOOFOO

GenTypeConstraints.scala

object GenTypeConstraints {
   type ||[A, B] = Either[A, B]
   implicit def any2Left[A, B](l: B): Either[B, A] = Left(l)
   implicit def any2Right[A, B](r: B): Either[A, B] = Right(r)
   def main(args: Array[String]) {
     println(f(1))
     println(f("FOO"))
     // compilation error println(f(1.0D))
   }
   def f[T](v: T)(implicit ev: T => (String || Int)): String = {
     ev(v) match {
       case Left(s) => s + s
       case Right(i) => (i + 1).toString
     }
   }
}