Clarified and expanded which Builders were reusable

This additionally fixes both SI-8648 and SI-9564.

Added documentation to Builder to clarify that in general Builders are NOT reusable.

Altered implementation of GrowingBuilder to use Growable instance's clear (not valid for a reusable builder, but this one isn't reusable).

Added a new marker trait ReusableBuilder that specifies that these builders should be reusable.  This trait overrides the clear and result methods while leaving them abstract in order to supply appropriate scaladoc.

Made all Array builders Reusable in all cases (by setting capacity to 0 if the original array is returned).  (Fixed a poor implmentation of Array[Unit] builder along the way.)

Documented which other builders were already reusable (maps, sets, Vector, LazyBuilder, StringBuilder, ListBuffer, etc.).

1 files changed, 4 insertions, 2 deletions

diff --git a/src/library/scala/collection/immutable/ListSet.scala b/src/library/scala/collection/immutable/ListSet.scala
index a65e25ed6e..98b91f7c84 100644
--- a/src/library/scala/collection/immutable/ListSet.scala
+++ b/src/library/scala/collection/immutable/ListSet.scala
@@ -12,7 +12,7 @@ package immutable
 
 import generic._
 import scala.annotation.tailrec
-import mutable.Builder
+import mutable.{Builder, ReusableBuilder}
 
 /** $factoryInfo
  *  @define Coll immutable.ListSet
@@ -32,8 +32,10 @@ object ListSet extends ImmutableSetFactory[ListSet] {
    *  a time to a list backed set puts the "squared" in N^2.  There is a
    *  temporary space cost, but it's improbable a list backed set could
    *  become large enough for this to matter given its pricy element lookup.
+   *
+   *  This builder is reusable.
    */
-  class ListSetBuilder[Elem](initial: ListSet[Elem]) extends Builder[Elem, ListSet[Elem]] {
+  class ListSetBuilder[Elem](initial: ListSet[Elem]) extends ReusableBuilder[Elem, ListSet[Elem]] {
     def this() = this(empty[Elem])
     protected val elems = (new mutable.ListBuffer[Elem] ++= initial).reverse
     protected val seen  = new mutable.HashSet[Elem] ++= initial