From cf53536f9e1b668e9e05c280db84ef2eb502765c Mon Sep 17 00:00:00 2001
From: Paul Phillips <paulp@improving.org>
Date: Wed, 28 Oct 2009 14:15:32 +0000
Subject: The final, tear-inducingly simple implementatio...

The final, tear-inducingly simple implementation of shape preserving
shuffle.
---
 src/library/scala/util/Random.scala | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/src/library/scala/util/Random.scala b/src/library/scala/util/Random.scala
index d22b3eca61..54feb8ac72 100644
--- a/src/library/scala/util/Random.scala
+++ b/src/library/scala/util/Random.scala
@@ -111,14 +111,13 @@ object Random extends Random
   import collection.mutable.ArrayBuffer
   import collection.generic.CanBuildFrom
 
-  /** Returns a new sequence in random order.
-   *  @param  seq   the sequence to shuffle
-   *  @return       the shuffled sequence
+  /** Returns a new collection of the same type in a randomly chosen order.
+   *
+   *  @param  coll    the Traversable to shuffle
+   *  @return         the shuffled Traversable
    */
-  def shuffle[T, CC[_] <: Traversable[_]](seq: CC[T])(implicit bf: CanBuildFrom[CC[T], T, CC[T]]): CC[T] = {
-    val builder = bf(seq)
-    val buf = new ArrayBuffer[T]
-    seq foreach (x => buf += x.asInstanceOf[T]) // why is this cast necessary?
+  def shuffle[T, CC[X] <: Traversable[X]](coll: CC[T])(implicit bf: CanBuildFrom[CC[T], T, CC[T]]): CC[T] = {
+    val buf = new ArrayBuffer[T] ++ coll
 
     def swap(i1: Int, i2: Int) {
       val tmp = buf(i1)
@@ -131,6 +130,6 @@ object Random extends Random
       swap(n - 1, k)
     }
 
-    bf(seq) ++= buf result
+    bf(coll) ++= buf result
   }
 }
-- 
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