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diff --git a/src/library/scala/collection/immutable/DefaultMap.scala b/src/library/scala/collection/immutable/DefaultMap.scala
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+++ b/src/library/scala/collection/immutable/DefaultMap.scala
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+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2003-2010, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+// $Id: DefaultMap.scala 20028 2009-12-07 11:49:19Z cunei $
+
+
+package scala.collection
+package immutable
+
+import generic._
+
+/** <p>
+ *    A default map which implements the <code>updated</code> and <code>-</code>
+ *    methods of maps.<br/>
+ *    Instances that inherit from <code>DefaultMap[A, B]</code> still have to
+ *    define:
+ *  </p><pre>
+ *    <b>def</b> get(key: A): Option[B]
+ *    <b>def</b> iterator: Iterator[(A, B)]</pre>
+ *  <p>
+ *    It refers back to the original map.
+ *  </p>
+ *  <p>
+ *    It might also be advisable to override <code>foreach</code> or
+ *    <code>size</code> if efficient implementations can be found.
+ *  </p>
+ *
+ *  @since 2.8
+ */
+trait DefaultMap[A, +B] extends Map[A, B] { self =>
+
+  /** A default implementation which creates a new immutable map.
+   */
+  override def +[B1 >: B](kv: (A, B1)): Map[A, B1] = {
+    val b = Map.newBuilder[A, B1]
+    b ++= this
+    b += ((kv._1, kv._2))
+    b.result
+  }
+
+  /** A default implementation which creates a new immutable map.
+   */
+  override def - (key: A): Map[A, B] = {
+    val b = newBuilder
+    b ++= this filter (key !=)
+    b.result
+  }
+}