Consistency work on Addable and Growable.

Seq-derived classes. Creating GrowingBuilder to complement AddingBuilder
on classes with += but not +. Fixed some inconsistencies I came across
in the process. No review.

1 files changed, 30 insertions, 0 deletions

diff --git a/src/library/scala/collection/mutable/GrowingBuilder.scala b/src/library/scala/collection/mutable/GrowingBuilder.scala
new file mode 100644
index 0000000000..259df9a434
--- /dev/null
+++ b/src/library/scala/collection/mutable/GrowingBuilder.scala
@@ -0,0 +1,30 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2003-2010, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+package scala.collection
+package mutable
+
+import generic._
+
+/** The canonical builder for collections that are growable, i.e. that support an
+ *  efficient `+=` method which adds an element to the collection.  It is
+ *  almost identical to AddingBuilder, but necessitated by the existence of
+ *  classes which are Growable but not Addable, which is a result of covariance
+ *  interacting surprisingly with any2stringadd thus driving '+' out of the Seq
+ *  hierachy.  The tendrils of original sin should never be underestimated.
+ *
+ *  @author Paul Phillips
+ *  @version 2.8
+ *  @since 2.8
+ */
+class GrowingBuilder[Elem, To <: Growable[Elem]](empty: To) extends Builder[Elem, To] {
+  protected var elems: To = empty
+  def +=(x: Elem): this.type = { elems += x; this }
+  def clear() { elems = empty }
+  def result: To = elems
+}