Nullable types in Scala

Nullable.scala

object Nullable {
  sealed trait NullableTag
  type Nullable[A] = A with NullableTag

  def nullAs[B]: Nullable[B] =
    null.asInstanceOf[Nullable[B]]

  implicit class ToNullable[A](val a: A) extends AnyVal {
    def `?`: Nullable[A] = a.asInstanceOf[Nullable[A]]
  }

  implicit class NullableOps[A](val a: Nullable[A]) extends AnyVal {
    def map[B](f: A => B): Nullable[B] =
      if(a == null) {
        nullAs[B]
      } else 
        f(a).?

    def flatMap[B](f: A => Nullable[B]): Nullable[B] =
      if(a == null)
        nullAs[B]
      else
        f(a).?

    def fold[B](empty: B)(full: A => B): B =
      if(a == null)
        empty
      else
        full(a)

    def getOrElse(empty: A): A =
      if(a == null)
        empty
      else
        a
  }
}

object Examples {
  import Nullable._

  def notNull =
    ("hi").? map (_ ++ " there") flatMap (a => if(a.length < 2) null else "dawg".?) getOrElse "dang"

  def isNull =
    ("").? map (_ ++ "") flatMap (a => if(a.length < 2) null else "yeah".?) getOrElse "dang"
}