union-types.scala

class Cell[T](value: T) {
  var other: T = value
}
object Test {
  def g[T, U](x: T, y: U) = if (util.Random.nextBoolean) x else y
  def f1 = g(1f, "abc")
  def f2 = g(1: Byte, "abc")
  def f3 = g(f1, f2)

  /*** Inferred return types:
  def g[T, U](x: T, y: U): T|U
  def f1: Float|String
  def f2: Byte|String
  def f3: String|Float|Byte
  ***/

  def main(args: Array[String]): Unit = {
    val x = new Cell(f3)
    x.other = 1f          // ok ( Float <:< Byte|Float|String)
    x.other = (1: Byte)   // ok (  Byte <:< Byte|Float|String)
    x.other = "def"       // ok (String <:< Byte|Float|String)
    x.other = 1d          // nope
    // a.scala:15: error: type mismatch;
    //  found   : Double(1.0)
    //  required: Byte|Float|String
    //     x.other = 1d
    //               ^
  }
}