Proposed implementation of 'unlift' on Function...

Proposed implementation of 'unlift' on Function1, the inverse function
of PartialFunction#lift. Review by rytz and other interested parties.
References #3825, but not closing until this is further considered.

1 files changed, 16 insertions, 1 deletions

diff --git a/src/library/scala/Function1.scala b/src/library/scala/Function1.scala
index a6a6fa2828..beac376f4e 100644
--- a/src/library/scala/Function1.scala
+++ b/src/library/scala/Function1.scala
@@ -7,7 +7,7 @@
 \*                                                                      */
 
 
-// generated by genprod on Thu Apr 29 17:52:16 CEST 2010 (with fancy comment) (with extra methods)
+// generated by genprod on Thu Sep 09 09:06:40 PDT 2010 (with fancy comment) (with extra methods)
 
 package scala
 
@@ -47,4 +47,19 @@ trait Function1[@specialized(scala.Int, scala.Long, scala.Float, scala.Double) -
    */
   def andThen[A](g: R => A): T1 => A = { x => g(apply(x)) }
 
+  /** Turns a function A => Option[B] into a PartialFunction[A, B].  Important note:
+   *  this transformation implies the original function will be called 2 or more
+   *  times on each logical invocation, because the only way to supply an implementation
+   *  of isDefinedAt is to call the function and examine the return value.
+   *
+   *  @see     PartialFunction#lift
+   *  @return  a partial function which is defined for those inputs
+   *           where this function returns Some(_) and undefined where
+   *           this function returns None.
+   */
+  def unlift[R1](implicit ev: R <:< Option[R1]): PartialFunction[T1, R1] = new PartialFunction[T1, R1] {
+    def apply(x: T1): R1 = ev(Function1.this.apply(x)).get
+    def isDefinedAt(x: T1): Boolean = Function1.this.apply(x).isDefined
+    override def lift = Function1.this.asInstanceOf[T1 => Option[R1]]
+  }
 }