1 files changed, 118 insertions, 0 deletions

diff --git a/src/library/scala/collection/immutable/HashSet.scala b/src/library/scala/collection/immutable/HashSet.scala
new file mode 100755
index 0000000000..aa4d832537
--- /dev/null
+++ b/src/library/scala/collection/immutable/HashSet.scala
@@ -0,0 +1,118 @@
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2003-2006, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |                                         **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
+
+// $Id: HashSet.scala 9554 2007-01-04 16:30:16 +0000 (Thu, 04 Jan 2007) odersky $
+package scala.collection.immutable
+
+object HashSet {
+
+  /** The empty set of this type.
+   */
+  def empty[A] = new HashSet[A]
+
+  /** The canonical factory for this type
+   */
+  def apply[A, B](elems: A*) = empty[A] ++ elems
+}
+
+[serializable]
+class HashSet[A] extends Set[A] with mutable.FlatHashTable[A] {
+  protected var later: HashSet[A] = null
+  protected var changedElem: A = _
+  protected var deleted: Boolean = _
+
+  def empty[C]: Set[C] = new EmptySet[C]
+
+  def contains(elem: A): Boolean = {
+    var m = this
+    var cnt = 0
+    while (m.later != null) {
+      if (elem == m.changedElem) return m.deleted
+      cnt = cnt + 1
+      m = m.later
+    }
+    if (cnt > logLimit) makeCopy(m)
+    m.containsEntry(elem)
+  }
+
+  def + (elem: A): Set[A] = {
+    makeCopyIfUpdated()
+    if (containsEntry(elem)) this
+    else {
+      markUpdated(elem, false)
+      later addEntry elem
+      later
+    }
+  }
+
+  def - (elem: A): Set[A] = {
+    makeCopyIfUpdated()
+    if (!containsEntry(elem)) this
+    else {
+      markUpdated(elem, true)
+      later removeEntry elem
+      later
+    }
+  }
+
+  override def size: Int = {
+    var m = this
+    var cnt = 0
+    var s = tableSize
+    while (m.later != null) {
+      if (m.deleted) s = s + 1 else s = s - 1
+      cnt = cnt + 1
+      m = m.later
+    }
+    if (cnt > logLimit) makeCopy(m)
+    s
+  }
+
+  override def elements = {
+    makeCopyIfUpdated()
+    super.elements
+  }
+
+  private def logLimit: Int = Math.sqrt(table.length.toDouble).toInt
+
+  private def markUpdated(elem: A, del: Boolean) {
+    val lv = loadFactor
+    later = new HashSet[A] {
+      override def initialSize = 0
+      override def loadFactor = lv
+      table     = HashSet.this.table
+      tableSize = HashSet.this.tableSize
+      threshold = HashSet.this.threshold
+    }
+    changedElem = elem
+    deleted = del
+  }
+
+  private def makeCopy(last: HashSet[A]) {
+    def undo(m: HashSet[A]) {
+      if (m ne last) {
+        undo(m.later)
+        if (m.deleted) addEntry(changedElem)
+        else removeEntry(changedElem)
+      }
+    }
+    table = new Array[AnyRef](last.table.length)
+    Array.copy(last.table, 0, table, 0, table.length)
+    tableSize = last.tableSize
+    threshold = last.threshold
+    undo(this)
+    later = null
+  }
+
+  private def makeCopyIfUpdated() {
+    var m = this
+    while (m.later != null) m = m.later
+    if (m ne this) makeCopy(m)
+  }
+}
+