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, 67 insertions, 0 deletions

diff --git a/test/files/run/view-iterator-stream.scala b/test/files/run/view-iterator-stream.scala
new file mode 100644
index 0000000000..5ac299a34d
--- /dev/null
+++ b/test/files/run/view-iterator-stream.scala
@@ -0,0 +1,67 @@
+import scala.collection.{ mutable, immutable, generic }
+import collection.TraversableView
+
+object Test {
+  type PerturberFn[T] = TraversableOnce[T] => TraversableOnce[T]
+  lazy val Id = new Perturber(Nil, identity[TraversableOnce[Int]] _) { }
+  class Perturber(val labels: List[String], val f: PerturberFn[Int]) extends PerturberFn[Int] {
+    def apply(xs: TraversableOnce[Int]): TraversableOnce[Int] = f(xs)
+    def show(xs: TraversableOnce[Int]): String = {
+      val res       = f(xs)
+      val resString = "" + res
+      val rest      = res.toTraversable
+      val failed    = (rest take 100).size == 100
+
+      "%-45s %-30s %s".format(toString, resString,
+        if (failed) "<failed>" else rest.mkString(" ")
+      )
+    }
+    def and(g: Perturber): Perturber =
+      new Perturber(this.labels ++ g.labels, f andThen g.f)
+
+    override def toString = labels mkString " -> "
+  }
+  object Perturber {
+    def apply(label: String, f: PerturberFn[Int]) = new Perturber(List(label), f)
+  }
+
+  def naturals = Stream from 1
+  val toV : Perturber = Perturber("view", _.toTraversable.view)
+  val toI : Perturber = Perturber("toIterator", _.toIterator)
+  val toS : Perturber = Perturber("toStream", _.toStream)
+  val toIS : Perturber = Perturber("toIndexedSeq", _.toIndexedSeq)
+
+  def p(ps: Perturber*): Perturber = if (ps.isEmpty) Id else ps.reduceLeft(_ and _)
+  def drop(n: Int): Perturber = Perturber("drop " + n, _.toIterator drop n)
+  def take(n: Int): Perturber = Perturber("take " + n, _.toIterator take n)
+  def slice(from: Int, until: Int): Perturber =
+    Perturber(
+      "slice(%d, %d)".format(from, until),
+      _.toTraversable.slice(from, until)
+    )
+
+  val fns = List[Perturber](toV, toI, toS, toIS)
+
+  def tds(n: Int): Perturber = p(drop(n), take(n / 2), slice(1, n / 4))
+  def dts(n: Int): Perturber = p(take(n), drop(n / 2), slice(1, n / 4))
+  def sdt(n: Int): Perturber = p(slice(n, n * 2), drop(n / 2), take(n / 4))
+  def std(n: Int): Perturber = p(slice(n, n * 2), take(n / 2), drop(n / 4))
+
+  val transforms = (fns.permutations map (xs => p(xs take 3: _*))).toList.distinct
+  def mkOps(n: Int) = List[Perturber](tds(n), dts(n), sdt(n), std(n))
+  def runOps(n: Int) = {
+    val xs: List[(String, List[String])] = mkOps(n) map { op =>
+      ("" + op, transforms map (_ show op(naturals)) sorted)
+    }
+    for ((k, v) <- xs) {
+      println("\n** " + k + " **\n")
+      println("-------------------")
+      v foreach println
+    }
+    ()
+  }
+
+  def main(args: Array[String]): Unit = {
+    runOps(20)
+  }
+}