1 files changed, 45 insertions, 0 deletions
diff --git a/src/library/scalax/collection/immutable/DefaultSet.scala b/src/library/scalax/collection/immutable/DefaultSet.scala
new file mode 100644
index 0000000000..a9ce3fb3df
--- /dev/null
+++ b/src/library/scalax/collection/immutable/DefaultSet.scala
@@ -0,0 +1,45 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2003-2009, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+// $Id: HashSet.scala 16884 2009-01-09 16:52:09Z cunei $
+
+package scalax.collection.immutable
+
+import generic.SetTemplate
+
+/** A default implementation of immutable sets.
+ *  This is currently implemented as a proxy for an immutable HashSet,
+ *  except that its builder returns specialized representations EmptySet,Set1,..., Set4
+ *  for sets of size <= 4.
+ */
+class DefaultSet[A] private (hset: HashSet[A])
+  extends Set[A]
+     with SetTemplate[Set, A] {
+
+  def this() = this(new HashSet[A])
+
+  def contains(elem: A): Boolean = hset.contains(elem)
+
+  def + (elem: A): Set[A] = hset + elem
+
+  /** Keeps underlying HashSet representation, but switches back to EmptySet if
+   *  result does not contain any elements
+   */
+  def - (elem: A): Set[A] = {
+    val hset1 = hset - elem
+    if (hset1.isEmpty) new EmptySet[A]
+    else new DefaultSet(hset)
+  }
+
+  def size: Int = hset.size
+
+  def elements: Iterator[A] = hset.elements
+
+  override def foreach(f: A => Unit): Unit = hset.foreach(f)
+}
+