Hard to explain garbage led me to this innocent...

Hard to explain garbage led me to this innocent seeming change. Not that
innocent. A function like this should create no garbage:

  final def f[T](xs: List[T], num: Int) {
    if (num > 0) f(Nil ::: xs ::: Nil, num - 1)
  }

Instead it was creating a lot.  No review.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/library/scala/collection/immutable/List.scala b/src/library/scala/collection/immutable/List.scala
index 5446b25888..563f14eac6 100644
--- a/src/library/scala/collection/immutable/List.scala
+++ b/src/library/scala/collection/immutable/List.scala
@@ -75,6 +75,7 @@ sealed abstract class List[+A] extends LinearSeq[A]
    */
   def :::[B >: A](prefix: List[B]): List[B] =
     if (isEmpty) prefix
+    else if (prefix.isEmpty) this
     else (new ListBuffer[B] ++= prefix).prependToList(this)
 
   /** Adds the elements of a given list in reverse order in front of this list.