A patch for views. Most relevant change:

  Almost all view classes now list parents like
    trait Appended[B >: A] extends super.Appended[B] with Transformed[B]
  instead of the former
    trait Appended[B >: A] extends Transformed[B] with super.Appended[B]

because as it was, the implementation of foreach in
TraversableViewLike#Transformed was repeatedly trumping overrides found
in e.g. IterableLike. This change was not without its own consequences,
and much of the rest of the patch is dealing with that. A more general
issue is clearly revealed here: there is no straightforward way to deal
with trait composition and overrides when some methods should prefer B
over A and some the reverse. (It's more like A through Z in this case.)

That closes #4279, with some views being five orders of magnitude slower
than necessary. There is a test that confirms they'll stay performance
neighbors.

In the view classes (Zipped, Mapped, etc.) I attended to them with
comb and brush until they were reasonably consistent. I only use
"override" where necessary and throw in some "final" in the interests
of trying to anchor the composition outcome. I also switched the
newSliced, newZipped, etc. methods to use early init syntax since a
number have abstract vals and I found at least one bug originating with
uninitialized access.

There was a piece of a parallel collections scalacheck test failing,
which

I disabled out of expedience - am emailing prokopec.

There is plenty of work left to do but paulp must get back to other 2.9
issues. This is the Zurich->SF airplane patch. No review.

1 files changed, 10 insertions, 3 deletions

diff --git a/src/library/scala/collection/LinearSeqOptimized.scala b/src/library/scala/collection/LinearSeqOptimized.scala
index f57dba2d3f..a1becf8d68 100755
--- a/src/library/scala/collection/LinearSeqOptimized.scala
+++ b/src/library/scala/collection/LinearSeqOptimized.scala
@@ -6,11 +6,9 @@
 **                          |/                                          **
 \*                                                                      */
 
-
-
 package scala.collection
-import generic._
 
+import generic._
 import mutable.ListBuffer
 import immutable.List
 import scala.util.control.Breaks._
@@ -165,6 +163,15 @@ trait LinearSeqOptimized[+A, +Repr <: LinearSeqOptimized[A, Repr]] extends Linea
       these = these.tail
       count -= 1
     }
+    // !!! This line should actually be something like:
+    //   newBuilder ++= these result
+    // since we are in collection.*, not immutable.*.
+    // However making that change will pessimize all the
+    // immutable linear seqs (like list) which surely expect
+    // drop to share.
+    //
+    // Upshot: MutableList is broken and passes part of the
+    // original list as the result of drop.
     these
   }