Discovered bug in mapConserve introduced in r23...

Discovered bug in mapConserve introduced in r23038 when a tail recursive
version was submitted. I am optimistic this is a player in recent
performance degradation based on the timing of the commit and the fact
that I was examining mapConserve because of info from my homemade
profiler. (But it's late and I only just found it, so I'll be the last
to know.) Review by odersky.

1 files changed, 1 insertions, 3 deletions

diff --git a/src/library/scala/collection/immutable/List.scala b/src/library/scala/collection/immutable/List.scala
index 8c018912c2..f717d516aa 100644
--- a/src/library/scala/collection/immutable/List.scala
+++ b/src/library/scala/collection/immutable/List.scala
@@ -99,8 +99,6 @@ sealed abstract class List[+A] extends LinearSeq[A]
    *  Like `xs map f`, but returns `xs` unchanged if function
    *  `f` maps all elements to themselves (wrt eq).
    *
-   *  Note: Unlike `map`, `mapConserve` is not tail-recursive.
-   *
    *  @param f      the function to apply to each element.
    *  @tparam B     the element type of the returned collection.
    *  @return       a list resulting from applying the given function
@@ -118,7 +116,7 @@ sealed abstract class List[+A] extends LinearSeq[A]
         val head0 = pending.head
         val head1 = f(head0)
 
-        if (head1 == head0)
+        if (head1 eq head0.asInstanceOf[AnyRef])
           loop(mapped, unchanged, pending.tail)
         else {
           val b = if (mapped eq null) new ListBuffer[B] else mapped