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, 112 insertions, 0 deletions

diff --git a/test/files/run/view-iterator-stream.check b/test/files/run/view-iterator-stream.check
new file mode 100644
index 0000000000..2da02c865c
--- /dev/null
+++ b/test/files/run/view-iterator-stream.check
@@ -0,0 +1,112 @@
+
+** drop 20 -> take 10 -> slice(1, 5) **
+
+-------------------
+toIndexedSeq -> toIterator -> toStream        Stream(22, ?)                  22 23 24 25
+toIndexedSeq -> toIterator -> view            StreamView(...)                22 23 24 25
+toIndexedSeq -> toStream -> toIterator        non-empty iterator             22 23 24 25
+toIndexedSeq -> toStream -> view              StreamView(...)                22 23 24 25
+toIndexedSeq -> view -> toIterator            non-empty iterator             22 23 24 25
+toIndexedSeq -> view -> toStream              Stream(22, ?)                  22 23 24 25
+toIterator -> toIndexedSeq -> toStream        Stream(22, ?)                  22 23 24 25
+toIterator -> toIndexedSeq -> view            SeqView(...)                   22 23 24 25
+toIterator -> toStream -> toIndexedSeq        Vector(22, 23, 24, 25)         22 23 24 25
+toIterator -> toStream -> view                StreamView(...)                22 23 24 25
+toIterator -> view -> toIndexedSeq            Vector(22, 23, 24, 25)         22 23 24 25
+toIterator -> view -> toStream                Stream(22, ?)                  22 23 24 25
+toStream -> toIndexedSeq -> toIterator        non-empty iterator             22 23 24 25
+toStream -> toIndexedSeq -> view              SeqView(...)                   22 23 24 25
+toStream -> toIterator -> toIndexedSeq        Vector(22, 23, 24, 25)         22 23 24 25
+toStream -> toIterator -> view                StreamView(...)                22 23 24 25
+toStream -> view -> toIndexedSeq              Vector(22, 23, 24, 25)         22 23 24 25
+toStream -> view -> toIterator                non-empty iterator             22 23 24 25
+view -> toIndexedSeq -> toIterator            non-empty iterator             22 23 24 25
+view -> toIndexedSeq -> toStream              Stream(22, ?)                  22 23 24 25
+view -> toIterator -> toIndexedSeq            Vector(22, 23, 24, 25)         22 23 24 25
+view -> toIterator -> toStream                Stream(22, ?)                  22 23 24 25
+view -> toStream -> toIndexedSeq              Vector(22, 23, 24, 25)         22 23 24 25
+view -> toStream -> toIterator                non-empty iterator             22 23 24 25
+
+** take 20 -> drop 10 -> slice(1, 5) **
+
+-------------------
+toIndexedSeq -> toIterator -> toStream        Stream(12, ?)                  12 13 14 15
+toIndexedSeq -> toIterator -> view            StreamView(...)                12 13 14 15
+toIndexedSeq -> toStream -> toIterator        non-empty iterator             12 13 14 15
+toIndexedSeq -> toStream -> view              StreamView(...)                12 13 14 15
+toIndexedSeq -> view -> toIterator            non-empty iterator             12 13 14 15
+toIndexedSeq -> view -> toStream              Stream(12, ?)                  12 13 14 15
+toIterator -> toIndexedSeq -> toStream        Stream(12, ?)                  12 13 14 15
+toIterator -> toIndexedSeq -> view            SeqView(...)                   12 13 14 15
+toIterator -> toStream -> toIndexedSeq        Vector(12, 13, 14, 15)         12 13 14 15
+toIterator -> toStream -> view                StreamView(...)                12 13 14 15
+toIterator -> view -> toIndexedSeq            Vector(12, 13, 14, 15)         12 13 14 15
+toIterator -> view -> toStream                Stream(12, ?)                  12 13 14 15
+toStream -> toIndexedSeq -> toIterator        non-empty iterator             12 13 14 15
+toStream -> toIndexedSeq -> view              SeqView(...)                   12 13 14 15
+toStream -> toIterator -> toIndexedSeq        Vector(12, 13, 14, 15)         12 13 14 15
+toStream -> toIterator -> view                StreamView(...)                12 13 14 15
+toStream -> view -> toIndexedSeq              Vector(12, 13, 14, 15)         12 13 14 15
+toStream -> view -> toIterator                non-empty iterator             12 13 14 15
+view -> toIndexedSeq -> toIterator            non-empty iterator             12 13 14 15
+view -> toIndexedSeq -> toStream              Stream(12, ?)                  12 13 14 15
+view -> toIterator -> toIndexedSeq            Vector(12, 13, 14, 15)         12 13 14 15
+view -> toIterator -> toStream                Stream(12, ?)                  12 13 14 15
+view -> toStream -> toIndexedSeq              Vector(12, 13, 14, 15)         12 13 14 15
+view -> toStream -> toIterator                non-empty iterator             12 13 14 15
+
+** slice(20, 40) -> drop 10 -> take 5 **
+
+-------------------
+toIndexedSeq -> toIterator -> toStream        Stream(31, ?)                  31 32 33 34 35
+toIndexedSeq -> toIterator -> view            StreamView(...)                31 32 33 34 35
+toIndexedSeq -> toStream -> toIterator        non-empty iterator             31 32 33 34 35
+toIndexedSeq -> toStream -> view              StreamView(...)                31 32 33 34 35
+toIndexedSeq -> view -> toIterator            non-empty iterator             31 32 33 34 35
+toIndexedSeq -> view -> toStream              Stream(31, ?)                  31 32 33 34 35
+toIterator -> toIndexedSeq -> toStream        Stream(31, ?)                  31 32 33 34 35
+toIterator -> toIndexedSeq -> view            SeqView(...)                   31 32 33 34 35
+toIterator -> toStream -> toIndexedSeq        Vector(31, 32, 33, 34, 35)     31 32 33 34 35
+toIterator -> toStream -> view                StreamView(...)                31 32 33 34 35
+toIterator -> view -> toIndexedSeq            Vector(31, 32, 33, 34, 35)     31 32 33 34 35
+toIterator -> view -> toStream                Stream(31, ?)                  31 32 33 34 35
+toStream -> toIndexedSeq -> toIterator        non-empty iterator             31 32 33 34 35
+toStream -> toIndexedSeq -> view              SeqView(...)                   31 32 33 34 35
+toStream -> toIterator -> toIndexedSeq        Vector(31, 32, 33, 34, 35)     31 32 33 34 35
+toStream -> toIterator -> view                StreamView(...)                31 32 33 34 35
+toStream -> view -> toIndexedSeq              Vector(31, 32, 33, 34, 35)     31 32 33 34 35
+toStream -> view -> toIterator                non-empty iterator             31 32 33 34 35
+view -> toIndexedSeq -> toIterator            non-empty iterator             31 32 33 34 35
+view -> toIndexedSeq -> toStream              Stream(31, ?)                  31 32 33 34 35
+view -> toIterator -> toIndexedSeq            Vector(31, 32, 33, 34, 35)     31 32 33 34 35
+view -> toIterator -> toStream                Stream(31, ?)                  31 32 33 34 35
+view -> toStream -> toIndexedSeq              Vector(31, 32, 33, 34, 35)     31 32 33 34 35
+view -> toStream -> toIterator                non-empty iterator             31 32 33 34 35
+
+** slice(20, 40) -> take 10 -> drop 5 **
+
+-------------------
+toIndexedSeq -> toIterator -> toStream        Stream(26, ?)                  26 27 28 29 30
+toIndexedSeq -> toIterator -> view            StreamView(...)                26 27 28 29 30
+toIndexedSeq -> toStream -> toIterator        non-empty iterator             26 27 28 29 30
+toIndexedSeq -> toStream -> view              StreamView(...)                26 27 28 29 30
+toIndexedSeq -> view -> toIterator            non-empty iterator             26 27 28 29 30
+toIndexedSeq -> view -> toStream              Stream(26, ?)                  26 27 28 29 30
+toIterator -> toIndexedSeq -> toStream        Stream(26, ?)                  26 27 28 29 30
+toIterator -> toIndexedSeq -> view            SeqView(...)                   26 27 28 29 30
+toIterator -> toStream -> toIndexedSeq        Vector(26, 27, 28, 29, 30)     26 27 28 29 30
+toIterator -> toStream -> view                StreamView(...)                26 27 28 29 30
+toIterator -> view -> toIndexedSeq            Vector(26, 27, 28, 29, 30)     26 27 28 29 30
+toIterator -> view -> toStream                Stream(26, ?)                  26 27 28 29 30
+toStream -> toIndexedSeq -> toIterator        non-empty iterator             26 27 28 29 30
+toStream -> toIndexedSeq -> view              SeqView(...)                   26 27 28 29 30
+toStream -> toIterator -> toIndexedSeq        Vector(26, 27, 28, 29, 30)     26 27 28 29 30
+toStream -> toIterator -> view                StreamView(...)                26 27 28 29 30
+toStream -> view -> toIndexedSeq              Vector(26, 27, 28, 29, 30)     26 27 28 29 30
+toStream -> view -> toIterator                non-empty iterator             26 27 28 29 30
+view -> toIndexedSeq -> toIterator            non-empty iterator             26 27 28 29 30
+view -> toIndexedSeq -> toStream              Stream(26, ?)                  26 27 28 29 30
+view -> toIterator -> toIndexedSeq            Vector(26, 27, 28, 29, 30)     26 27 28 29 30
+view -> toIterator -> toStream                Stream(26, ?)                  26 27 28 29 30
+view -> toStream -> toIndexedSeq              Vector(26, 27, 28, 29, 30)     26 27 28 29 30
+view -> toStream -> toIterator                non-empty iterator             26 27 28 29 30