1 files changed, 47 insertions, 13 deletions
diff --git a/src/library/scala/collection/immutable/HashMap.scala b/src/library/scala/collection/immutable/HashMap.scala
index 3e482f1369..627f723cb0 100644
--- a/src/library/scala/collection/immutable/HashMap.scala
+++ b/src/library/scala/collection/immutable/HashMap.scala
@@ -33,8 +33,7 @@ import parallel.immutable.ParHashMap
  *  @define willNotTerminateInf
  */
 @SerialVersionUID(2L)
-@deprecatedInheritance("The implementation details of immutable hash maps make inheriting from them unwise.", "2.11.0")
-class HashMap[A, +B] extends AbstractMap[A, B]
+sealed class HashMap[A, +B] extends AbstractMap[A, B]
                         with Map[A, B]
                         with MapLike[A, B, HashMap[A, B]]
                         with Serializable
@@ -53,6 +52,9 @@ class HashMap[A, +B] extends AbstractMap[A, B]
   def get(key: A): Option[B] =
     get0(key, computeHash(key), 0)
 
+  override final def contains(key: A): Boolean =
+    contains0(key, computeHash(key), 0)
+
   override def updated [B1 >: B] (key: A, value: B1): HashMap[A, B1] =
     updated0(key, computeHash(key), 0, value, null, null)
 
@@ -65,6 +67,8 @@ class HashMap[A, +B] extends AbstractMap[A, B]
   def - (key: A): HashMap[A, B] =
     removed0(key, computeHash(key), 0)
 
+  override def tail: HashMap[A, B] = this - head._1
+
   override def filter(p: ((A, B)) => Boolean) = {
     val buffer = new Array[HashMap[A, B]](bufferSize(size))
     nullToEmpty(filter0(p, false, 0, buffer, 0))
@@ -91,7 +95,7 @@ class HashMap[A, +B] extends AbstractMap[A, B]
   import HashMap.{Merger, MergeFunction, liftMerger}
 
   private[collection] def get0(key: A, hash: Int, level: Int): Option[B] = None
-
+  protected def contains0(key: A, hash: Int, level: Int): Boolean = false
   private[collection] def updated0[B1 >: B](key: A, hash: Int, level: Int, value: B1, kv: (A, B1), merger: Merger[A, B1]): HashMap[A, B1] =
     new HashMap.HashMap1(key, hash, value, kv)
 
@@ -156,7 +160,10 @@ object HashMap extends ImmutableMapFactory[HashMap] with BitOperations.Int {
   implicit def canBuildFrom[A, B]: CanBuildFrom[Coll, (A, B), HashMap[A, B]] = new MapCanBuildFrom[A, B]
   def empty[A, B]: HashMap[A, B] = EmptyHashMap.asInstanceOf[HashMap[A, B]]
 
-  private object EmptyHashMap extends HashMap[Any, Nothing] { }
+  private object EmptyHashMap extends HashMap[Any, Nothing] { 
+    override def head: (Any, Nothing) = throw new NoSuchElementException("Empty Map")
+    override def tail: HashMap[Any, Nothing] = throw new NoSuchElementException("Empty Map")
+  }
 
   // utility method to create a HashTrieMap from two leaf HashMaps (HashMap1 or HashMapCollision1) with non-colliding hash code)
   private def makeHashTrieMap[A, B](hash0:Int, elem0:HashMap[A, B], hash1:Int, elem1:HashMap[A, B], level:Int, size:Int) : HashTrieMap[A, B] = {
@@ -181,6 +188,7 @@ object HashMap extends ImmutableMapFactory[HashMap] with BitOperations.Int {
     }
   }
 
+  @deprecatedInheritance("This class will be made final in a future release.", "2.12.2")
   class HashMap1[A,+B](private[collection] val key: A, private[collection] val hash: Int, private[collection] val value: (B @uV), private[collection] var kv: (A,B @uV)) extends HashMap[A,B] {
     override def size = 1
 
@@ -191,6 +199,8 @@ object HashMap extends ImmutableMapFactory[HashMap] with BitOperations.Int {
     override def get0(key: A, hash: Int, level: Int): Option[B] =
       if (hash == this.hash && key == this.key) Some(value) else None
 
+    override protected def contains0(key: A, hash: Int, level: Int): Boolean =
+      hash == this.hash && key == this.key
     private[collection] override def updated0[B1 >: B](key: A, hash: Int, level: Int, value: B1, kv: (A, B1), merger: Merger[A, B1]): HashMap[A, B1] =
       if (hash == this.hash && key == this.key ) {
         if (merger eq null) {
@@ -235,6 +245,9 @@ object HashMap extends ImmutableMapFactory[HashMap] with BitOperations.Int {
     override def get0(key: A, hash: Int, level: Int): Option[B] =
       if (hash == this.hash) kvs.get(key) else None
 
+    override protected def contains0(key: A, hash: Int, level: Int): Boolean =
+      hash == this.hash && kvs.contains(key)
+
     private[collection] override def updated0[B1 >: B](key: A, hash: Int, level: Int, value: B1, kv: (A, B1), merger: Merger[A, B1]): HashMap[A, B1] =
       if (hash == this.hash) {
         if ((merger eq null) || !kvs.contains(key)) new HashMapCollision1(hash, kvs.updated(key, value))
@@ -290,6 +303,7 @@ object HashMap extends ImmutableMapFactory[HashMap] with BitOperations.Int {
     }
   }
 
+  @deprecatedInheritance("This class will be made final in a future release.", "2.12.2")
   class HashTrieMap[A, +B](
     private[collection] val bitmap: Int,
     private[collection] val elems: Array[HashMap[A, B @uV]],
@@ -302,21 +316,41 @@ object HashMap extends ImmutableMapFactory[HashMap] with BitOperations.Int {
     override def size = size0
 
     override def get0(key: A, hash: Int, level: Int): Option[B] = {
+      // Note: this code is duplicated with `contains0`
+      val index = (hash >>> level) & 0x1f
+      if (bitmap == - 1) {
+        elems(index).get0(key, hash, level + 5)
+      } else {
+        val mask = (1 << index)
+        if ((bitmap & mask) != 0) {
+          val offset = Integer.bitCount(bitmap & (mask - 1))
+          elems(offset).get0(key, hash, level + 5)
+        } else {
+          None
+        }
+      }
+    }
+
+    override protected def contains0(key: A, hash: Int, level: Int): Boolean = {
+      // Note: this code is duplicated from `get0`
       val index = (hash >>> level) & 0x1f
-      val mask = (1 << index)
       if (bitmap == - 1) {
-        elems(index & 0x1f).get0(key, hash, level + 5)
-      } else if ((bitmap & mask) != 0) {
-        val offset = Integer.bitCount(bitmap & (mask-1))
-        elems(offset).get0(key, hash, level + 5)
-      } else
-        None
+        elems(index).contains0(key, hash, level + 5)
+      } else {
+        val mask = (1 << index)
+        if ((bitmap & mask) != 0) {
+          val offset = Integer.bitCount(bitmap & (mask - 1))
+          elems(offset).contains0(key, hash, level + 5)
+        } else {
+          false
+        }
+      }
     }
 
     private[collection] override def updated0[B1 >: B](key: A, hash: Int, level: Int, value: B1, kv: (A, B1), merger: Merger[A, B1]): HashMap[A, B1] = {
       val index = (hash >>> level) & 0x1f
       val mask = (1 << index)
-      val offset = Integer.bitCount(bitmap & (mask-1))
+      val offset = Integer.bitCount(bitmap & (mask - 1))
       if ((bitmap & mask) != 0) {
         val sub = elems(offset)
         val subNew = sub.updated0(key, hash, level + 5, value, kv, merger)
@@ -338,7 +372,7 @@ object HashMap extends ImmutableMapFactory[HashMap] with BitOperations.Int {
     override def removed0(key: A, hash: Int, level: Int): HashMap[A, B] = {
       val index = (hash >>> level) & 0x1f
       val mask = (1 << index)
-      val offset = Integer.bitCount(bitmap & (mask-1))
+      val offset = Integer.bitCount(bitmap & (mask - 1))
       if ((bitmap & mask) != 0) {
         val sub = elems(offset)
         val subNew = sub.removed0(key, hash, level + 5)