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, 2 insertions, 3 deletions

diff --git a/src/library/scala/collection/LinearSeqLike.scala b/src/library/scala/collection/LinearSeqLike.scala
index 6d346f3fe0..068c63432f 100644
--- a/src/library/scala/collection/LinearSeqLike.scala
+++ b/src/library/scala/collection/LinearSeqLike.scala
@@ -18,8 +18,7 @@ import scala.util.control.Breaks._
  *
  *  $linearSeqInfo
  *
- *  This trait just implements `iterator`
- *  in terms of `isEmpty, ``head`, and `tail`.
+ *  This trait just implements `iterator` in terms of `isEmpty, ``head`, and `tail`.
  *  However, see `LinearSeqOptimized` for an implementation trait that overrides operations
  *  to make them run faster under the assumption of fast linear access with `head` and `tail`.
  *
@@ -56,7 +55,7 @@ trait LinearSeqLike[+A, +Repr <: LinearSeqLike[A, Repr]] extends SeqLike[A, Repr
         val result = these.head; these = these.tail; result
       } else Iterator.empty.next
 
-    /** Have to clear these so the iterator is exhausted like
+    /** Have to clear `these` so the iterator is exhausted like
      *  it would be without the optimization.
      */
     override def toList: List[A] = {