From 6f881202be35c7d08ca73054594618cef19d8938 Mon Sep 17 00:00:00 2001
From: Paul Phillips <paulp@improving.org>
Date: Sun, 28 Aug 2011 00:13:17 +0000
Subject: Gave partial function an empty member.

---
 src/library/scala/PartialFunction.scala | 11 +++++++++--
 test/files/run/emptypf.check            |  3 +++
 test/files/run/emptypf.scala            | 14 ++++++++++++++
 3 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 test/files/run/emptypf.check
 create mode 100644 test/files/run/emptypf.scala

diff --git a/src/library/scala/PartialFunction.scala b/src/library/scala/PartialFunction.scala
index b8e20c2de1..51bb3dc93e 100644
--- a/src/library/scala/PartialFunction.scala
+++ b/src/library/scala/PartialFunction.scala
@@ -81,8 +81,15 @@ trait PartialFunction[-A, +B] extends (A => B) {
  *  @author  Paul Phillips
  *  @since   2.8
  */
-object PartialFunction
-{
+object PartialFunction {
+  private[this] final val empty_pf = new PartialFunction[Any, Nothing] {
+    def isDefinedAt(x: Any) = false
+    def apply(x: Any): Nothing = sys.error("undefined")
+    override def orElse[A1, B1](that: PartialFunction[A1, B1]): PartialFunction[A1, B1] = that
+    override def lift = (x: Any) => None
+  }
+  def empty[A, B] : PartialFunction[A, B] = empty_pf.asInstanceOf[PartialFunction[A, B]]
+
   /** Creates a Boolean test based on a value and a partial function.
    *  It behaves like a 'match' statement with an implied 'case _ => false'
    *  following the supplied cases.
diff --git a/test/files/run/emptypf.check b/test/files/run/emptypf.check
new file mode 100644
index 0000000000..f6c39921bc
--- /dev/null
+++ b/test/files/run/emptypf.check
@@ -0,0 +1,3 @@
+100
+3
+false
diff --git a/test/files/run/emptypf.scala b/test/files/run/emptypf.scala
new file mode 100644
index 0000000000..eb3e3e6380
--- /dev/null
+++ b/test/files/run/emptypf.scala
@@ -0,0 +1,14 @@
+object Test {
+  val f: PartialFunction[String, Int] = {
+    PartialFunction.empty[String, Int] orElse {
+      case "abc"  => 100
+      case s      => s.length
+    }
+  }
+
+  def main(args: Array[String]): Unit = {
+    println(f("abc"))
+    println(f("def"))
+    println(PartialFunction.empty[String, Int] isDefinedAt "abc")
+  }
+}
-- 
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