Implement the ensure and andThen methods on futures.

1 files changed, 56 insertions, 1 deletions

diff --git a/src/library/scala/concurrent/Future.scala b/src/library/scala/concurrent/Future.scala
index 29b17cf70a..1b20c91e49 100644
--- a/src/library/scala/concurrent/Future.scala
+++ b/src/library/scala/concurrent/Future.scala
@@ -155,7 +155,7 @@ self =>
     
     val p = newPromise[Throwable]
     
-    this onComplete {
+    onComplete {
       case Left(t) => p success t
       case Right(v) => p failure noSuchElem(v)
     }
@@ -377,6 +377,61 @@ self =>
     p.future
   }
   
+  /** Applies the side-effecting function to the result of this future, and returns
+   *  a new future with the result of this future.
+   *  
+   *  This method allows one to enforce that the callbacks are executed in a
+   *  specified order.
+   *  
+   *  Note that if one of the chained `andThen` callbacks throws
+   *  an exception, that exception is not propagated to the subsequent `andThen`
+   *  callbacks. Instead, the subsequent `andThen` callbacks are given the original
+   *  value of this future.
+   *  
+   *  The following example prints out `5`:
+   *  
+   *  {{{
+   *  val f = future { 5 }
+   *  f andThen {
+   *    case r => sys.error("runtime exception")
+   *  } andThen {
+   *    case Left(t) => println(t)
+   *    case Right(v) => println(v)
+   *  }
+   *  }}}
+   */
+  def andThen[U](pf: PartialFunction[Either[Throwable, T], U]): Future[T] = {
+    val p = newPromise[T]
+    
+    onComplete {
+      case r =>
+        try if (pf isDefinedAt r) pf(r)
+        finally p complete r
+    }
+    
+    p.future
+  }
+  
+  /** Executes a piece of code once this future is completed, regardless of whether
+   *  or not the future fails or succeeds, and returns a new future with the result of this
+   *  future.
+   *
+   *  This method allows one to enforce ordering.
+   *  
+   *  The below example always executes the `println` calls in order:
+   *  {{{
+   *  val f = future { 5 }
+   *  f ensure {
+   *    println("The value is available.")
+   *  } ensure {
+   *    println("The application can now end.")
+   *  }
+   *  }}}
+   */
+  def ensure[U](body: =>U): Future[T] = andThen {
+    case _ => body
+  }
+  
   /** Creates a new future which holds the result of either this future or `that` future, depending on
    *  which future was completed first.
    *