Fixes #3829. Review by extempore.

3 files changed, 34 insertions, 17 deletions

diff --git a/src/library/scala/collection/Map.scala b/src/library/scala/collection/Map.scala
index b48acd0c4e..ccf58b5a0b 100644
--- a/src/library/scala/collection/Map.scala
+++ b/src/library/scala/collection/Map.scala
@@ -30,6 +30,12 @@ import generic._
  */
 trait Map[A, +B] extends Iterable[(A, B)] with MapLike[A, B, Map[A, B]] {
   def empty: Map[A, B] = Map.empty
+
+  /** The same map with a given default function !!! todo: move to general maps? */
+  def withDefault[B1 >: B](d: A => B1): Map[A, B1] = new Map.WithDefault[A, B1](this, d)
+
+  /** The same map with a given default value */
+  def withDefaultValue[B1 >: B](d: B1): Map[A, B1] = new Map.WithDefault[A, B1](this, x => d)
 }
 
 /** $factoryInfo
@@ -41,4 +47,16 @@ object Map extends MapFactory[Map] {
 
   /** $mapCanBuildFromInfo */
   implicit def canBuildFrom[A, B]: CanBuildFrom[Coll, (A, B), Map[A, B]] = new MapCanBuildFrom[A, B]
+
+  class WithDefault[A, +B](underlying: Map[A, B], d: A => B) extends Map[A, B] {
+    override def size = underlying.size
+    def get(key: A) = underlying.get(key) orElse Some(default(key))
+    def iterator = underlying.iterator
+    override def empty = new WithDefault(underlying.empty, d)
+    override def updated[B1 >: B](key: A, value: B1): WithDefault[A, B1] = new WithDefault[A, B1](underlying.updated[B1](key, value), d)
+    override def + [B1 >: B](kv: (A, B1)): WithDefault[A, B1] = updated(kv._1, kv._2)
+    def - (key: A): WithDefault[A, B] = new WithDefault(underlying - key, d)
+    override def default(key: A): B = d(key)
+  }
+
 }
diff --git a/src/library/scala/collection/immutable/Map.scala b/src/library/scala/collection/immutable/Map.scala
index c65fb170cc..ef1f6b60ed 100644
--- a/src/library/scala/collection/immutable/Map.scala
+++ b/src/library/scala/collection/immutable/Map.scala
@@ -39,12 +39,6 @@ trait Map[A, +B] extends Iterable[(A, B)]
    */
   override def updated [B1 >: B](key: A, value: B1): Map[A, B1]
   def + [B1 >: B](kv: (A, B1)): Map[A, B1]
-
-  /** The same map with a given default function !!! todo: move to general maps? */
-  def withDefault[B1 >: B](d: A => B1): Map[A, B1] = new Map.WithDefault[A, B1](this, d)
-
-  /** The same map with a given default value */
-  def withDefaultValue[B1 >: B](d: B1): Map[A, B1] = new Map.WithDefault[A, B1](this, x => d)
 }
 
 /** $factoryInfo
@@ -58,17 +52,6 @@ object Map extends ImmutableMapFactory[Map] {
 
   def empty[A, B]: Map[A, B] = EmptyMap.asInstanceOf[Map[A, B]]
 
-  class WithDefault[A, +B](underlying: Map[A, B], d: A => B) extends Map[A, B] {
-    override def size = underlying.size
-    def get(key: A) = underlying.get(key) orElse Some(default(key))
-    def iterator = underlying.iterator
-    override def empty = new WithDefault(underlying.empty, d)
-    override def updated[B1 >: B](key: A, value: B1): WithDefault[A, B1] = new WithDefault[A, B1](underlying.updated[B1](key, value), d)
-    def + [B1 >: B](kv: (A, B1)): WithDefault[A, B1] = updated(kv._1, kv._2)
-    def - (key: A): WithDefault[A, B] = new WithDefault(underlying - key, d)
-    override def default(key: A): B = d(key)
-  }
-
   @serializable
   private object EmptyMap extends Map[Any, Nothing] {
     override def size: Int = 0
diff --git a/src/library/scala/collection/mutable/Map.scala b/src/library/scala/collection/mutable/Map.scala
index 287069d04b..7a56862119 100644
--- a/src/library/scala/collection/mutable/Map.scala
+++ b/src/library/scala/collection/mutable/Map.scala
@@ -26,6 +26,12 @@ trait Map[A, B]
 
   override def empty: Map[A, B] = Map.empty
 
+  /** The same map with a given default function !!! todo: move to general maps? */
+  def withDefault(d: A => B): Map[A, B] = new Map.WithDefault[A, B](this, d)
+
+  /** The same map with a given default value */
+  def withDefaultValue(d: B): Map[A, B] = new Map.WithDefault[A, B](this, x => d)
+
   /** Return a read-only projection of this map.  !!! or just use an (immutable) MapProxy?
   def readOnly : scala.collection.Map[A, B] = new scala.collection.Map[A, B] {
     override def size = self.size
@@ -49,5 +55,15 @@ object Map extends MutableMapFactory[Map] {
   implicit def canBuildFrom[A, B]: CanBuildFrom[Coll, (A, B), Map[A, B]] = new MapCanBuildFrom[A, B]
 
   def empty[A, B]: Map[A, B] = new HashMap[A, B]
+
+  class WithDefault[A, B](underlying: Map[A, B], d: A => B) extends collection.Map.WithDefault(underlying, d) with Map[A, B] {
+    override def += (kv: (A, B)) = {underlying += kv; this}
+    def -= (key: A) = {underlying -= key; this}
+    override def empty = new WithDefault(underlying.empty, d)
+    override def updated[B1 >: B](key: A, value: B1): WithDefault[A, B1] = new WithDefault[A, B1](underlying.updated[B1](key, value), d)
+    override def + [B1 >: B](kv: (A, B1)): WithDefault[A, B1] = updated(kv._1, kv._2)
+    override def - (key: A): WithDefault[A, B] = new WithDefault(underlying - key, d)
+  }
+
 }