Weak reference scala

gistfile1.scala

trait WkRef[+T >: Null <: AnyRef] extends WeakReference[T @uncheckedVariance] {
  def map[U >: Null <: AnyRef](f: T => U): WkRef[U] = if(isDefined) new WeakRef[U](f(get)) else WeakNone
  def flatMap[U >: Null <: AnyRef](f: T => WkRef[U]) = if(isDefined) f(get) else WeakNone
  def isDefined: Boolean
  def foreach[U](f: T => U) = if(isDefined) f(get)
  def filter(f: T => Boolean): WkRef[T] = if(isDefined && f(get)) this else WeakNone
}
object WkRef {
  def apply[T >: Null <: AnyRef](t: T) = t match {
    case null => WeakNone
    case _    => new WeakRef[T](t)
  }
}
class WeakRef[+T >: Null <: AnyRef](ref: T) extends WeakReference[T @uncheckedVariance](ref) with WkRef[T] {
  def isDefined = get != null
  override def toString = s"WeakRef(${get})}"
}

object WeakNone extends WeakReference[Null](null) with WkRef[Null]{
  def isDefined = false
  override def get = throw new NoSuchElementException
  override def toString = "WeakNone"
}