Collections refactoring.

1 files changed, 31 insertions, 0 deletions

diff --git a/src/library/scala/collection/mutable/MapBuilder.scala b/src/library/scala/collection/mutable/MapBuilder.scala
new file mode 100644
index 0000000000..bcbd50c44e
--- /dev/null
+++ b/src/library/scala/collection/mutable/MapBuilder.scala
@@ -0,0 +1,31 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2003-2009, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+// $Id$
+
+package scala.collection
+package mutable
+
+/** The canonical builder for immutable maps, working with the map's `+` method
+ *  to add new elements.
+ *  Collections are built from their `empty` element using this + method.
+ *  @param empty   The empty element of the collection.
+ */
+class MapBuilder[A, B, Coll <: scala.collection.Map[A, B] with scala.collection.MapLike[A, B, Coll]](empty: Coll)
+extends Builder[(A, B), Coll] {
+  protected var elems: Coll = empty
+  def +=(x: (A, B)): this.type = {
+    elems = (elems + x).asInstanceOf[Coll]
+      // the cast is necessary because right now we cannot enforce statically that
+      // for every map of type Coll, `+` yields again a Coll. With better support
+      // for hk-types we might be able to enforce this in the future, though.
+    this
+  }
+  def clear() { elems = empty }
+  def result: Coll = elems
+}