Fixes SI-6150 - backport to 2.10.x branch.

5 files changed, 47 insertions, 31 deletions

diff --git a/src/library/scala/collection/IndexedSeq.scala b/src/library/scala/collection/IndexedSeq.scala
index e30d2f07bb..63e5adf428 100644
--- a/src/library/scala/collection/IndexedSeq.scala
+++ b/src/library/scala/collection/IndexedSeq.scala
@@ -28,8 +28,14 @@ trait IndexedSeq[+A] extends Seq[A]
  *  @define coll indexed sequence
  *  @define Coll `IndexedSeq`
  */
-object IndexedSeq extends SeqFactory[IndexedSeq] {
-  implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, IndexedSeq[A]] = ReusableCBF.asInstanceOf[GenericCanBuildFrom[A]]
+object IndexedSeq extends IndexedSeqFactory[IndexedSeq] {
+  // A single CBF which can be checked against to identify
+  // an indexed collection type.
+  override val ReusableCBF: GenericCanBuildFrom[Nothing] = new GenericCanBuildFrom[Nothing] {
+    override def apply() = newBuilder[Nothing]
+  }
   def newBuilder[A]: Builder[A, IndexedSeq[A]] = immutable.IndexedSeq.newBuilder[A]
+  implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, IndexedSeq[A]] =
+    ReusableCBF.asInstanceOf[GenericCanBuildFrom[A]]
 }
 
diff --git a/src/library/scala/collection/generic/GenTraversableFactory.scala b/src/library/scala/collection/generic/GenTraversableFactory.scala
index d5edf5961e..a43862abaf 100644
--- a/src/library/scala/collection/generic/GenTraversableFactory.scala
+++ b/src/library/scala/collection/generic/GenTraversableFactory.scala
@@ -36,15 +36,12 @@ import scala.language.higherKinds
  *    @see GenericCanBuildFrom
  */
 abstract class GenTraversableFactory[CC[X] <: GenTraversable[X] with GenericTraversableTemplate[X, CC]]
-  extends GenericCompanion[CC] {
+extends GenericCompanion[CC] {
 
-  // A default implementation of GenericCanBuildFrom which can be cast
-  // to whatever is desired.
-  private class ReusableCBF extends GenericCanBuildFrom[Nothing] {
+  private[this] val ReusableCBFInstance: GenericCanBuildFrom[Nothing] = new GenericCanBuildFrom[Nothing] {
     override def apply() = newBuilder[Nothing]
   }
-  // Working around SI-4789 by using a lazy val instead of an object.
-  lazy val ReusableCBF: GenericCanBuildFrom[Nothing] = new ReusableCBF
+  def ReusableCBF: GenericCanBuildFrom[Nothing] = ReusableCBFInstance
 
   /** A generic implementation of the `CanBuildFrom` trait, which forwards
    *  all calls to `apply(from)` to the `genericBuilder` method of
diff --git a/src/library/scala/collection/generic/IndexedSeqFactory.scala b/src/library/scala/collection/generic/IndexedSeqFactory.scala
new file mode 100644
index 0000000000..200d033c2d
--- /dev/null
+++ b/src/library/scala/collection/generic/IndexedSeqFactory.scala
@@ -0,0 +1,21 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2003-2011, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+package scala.collection
+package generic
+
+import language.higherKinds
+
+/** A template for companion objects of IndexedSeq and subclasses thereof.
+ *
+ *  @since 2.10
+ */
+abstract class IndexedSeqFactory[CC[X] <: IndexedSeq[X] with GenericTraversableTemplate[X, CC]] extends SeqFactory[CC] {
+  override def ReusableCBF: GenericCanBuildFrom[Nothing] =
+    scala.collection.IndexedSeq.ReusableCBF.asInstanceOf[GenericCanBuildFrom[Nothing]]
+}
diff --git a/src/library/scala/collection/immutable/IndexedSeq.scala b/src/library/scala/collection/immutable/IndexedSeq.scala
index e98df46c9b..bf4ba3a381 100644
--- a/src/library/scala/collection/immutable/IndexedSeq.scala
+++ b/src/library/scala/collection/immutable/IndexedSeq.scala
@@ -31,11 +31,12 @@ trait IndexedSeq[+A] extends Seq[A]
  *  @define coll indexed sequence
  *  @define Coll `IndexedSeq`
  */
-object IndexedSeq extends SeqFactory[IndexedSeq] {
+object IndexedSeq extends IndexedSeqFactory[IndexedSeq] {
   class Impl[A](buf: ArrayBuffer[A]) extends AbstractSeq[A] with IndexedSeq[A] with Serializable {
     def length = buf.length
     def apply(idx: Int) = buf.apply(idx)
   }
-  implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, IndexedSeq[A]] = ReusableCBF.asInstanceOf[GenericCanBuildFrom[A]]
   def newBuilder[A]: Builder[A, IndexedSeq[A]] = Vector.newBuilder[A]
+  implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, IndexedSeq[A]] =
+    ReusableCBF.asInstanceOf[GenericCanBuildFrom[A]]
 }
diff --git a/src/library/scala/collection/immutable/Vector.scala b/src/library/scala/collection/immutable/Vector.scala
index dff221ad05..f083e80175 100644
--- a/src/library/scala/collection/immutable/Vector.scala
+++ b/src/library/scala/collection/immutable/Vector.scala
@@ -18,16 +18,10 @@ import scala.collection.parallel.immutable.ParVector
 
 /** Companion object to the Vector class
  */
-object Vector extends SeqFactory[Vector] {
-  private[collection] class VectorReusableCBF extends GenericCanBuildFrom[Nothing] {
-    override def apply() = newBuilder[Nothing]
-  }
-
-  private val VectorReusableCBF: GenericCanBuildFrom[Nothing] = new VectorReusableCBF
-
-  implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, Vector[A]] =
-    VectorReusableCBF.asInstanceOf[CanBuildFrom[Coll, A, Vector[A]]]
+object Vector extends IndexedSeqFactory[Vector] {
   def newBuilder[A]: Builder[A, Vector[A]] = new VectorBuilder[A]
+  implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, Vector[A]] =
+    ReusableCBF.asInstanceOf[GenericCanBuildFrom[A]]
   private[immutable] val NIL = new Vector[Nothing](0, 0, 0)
   override def empty[A]: Vector[A] = NIL
 }
@@ -137,20 +131,17 @@ override def companion: GenericCompanion[Vector] = Vector
 
   // SeqLike api
 
-  override def updated[B >: A, That](index: Int, elem: B)(implicit bf: CanBuildFrom[Vector[A], B, That]): That = bf match {
-    case _: Vector.VectorReusableCBF => updateAt(index, elem).asInstanceOf[That] // just ignore bf
-    case _ => super.updated(index, elem)(bf)
-  }
+  override def updated[B >: A, That](index: Int, elem: B)(implicit bf: CanBuildFrom[Vector[A], B, That]): That =
+    if (bf eq IndexedSeq.ReusableCBF) updateAt(index, elem).asInstanceOf[That] // just ignore bf
+    else super.updated(index, elem)(bf)
 
-  override def +:[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Vector[A], B, That]): That = bf match {
-    case _: Vector.VectorReusableCBF => appendFront(elem).asInstanceOf[That] // just ignore bf
-    case _ => super.+:(elem)(bf)
-  }
+  override def +:[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Vector[A], B, That]): That =
+    if (bf eq IndexedSeq.ReusableCBF) appendFront(elem).asInstanceOf[That] // just ignore bf
+    else super.+:(elem)(bf)
 
-  override def :+[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Vector[A], B, That]): That = bf match {
-    case _: Vector.VectorReusableCBF => appendBack(elem).asInstanceOf[That] // just ignore bf
-    case _ => super.:+(elem)(bf)
-  }
+  override def :+[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Vector[A], B, That]): That = 
+    if (bf eq IndexedSeq.ReusableCBF) appendBack(elem).asInstanceOf[That] // just ignore bf
+    else super.:+(elem)(bf)
 
   override def take(n: Int): Vector[A] = {
     if (n <= 0)