path: root/sources/scala/collection/immutable/ListSet.scala

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003, LAMP/EPFL                  **
**  __\ \/ /__/ __ |/ /__/ __ |                                         **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
** $Id$
\*                                                                      */

package scala.collection.immutable;


object ListSet {
    def Empty[A] = new ListSet[A];
}

/** This class implements immutable sets using a list-based data
 *  structure. Instances of <code>ListSet</code> represent
 *  empty sets; they can be either created by calling the constructor
 *  directly, or by applying the function <code>ListSet.Empty</code>.
 *
 *  @author  Matthias Zenger
 *  @version 1.0, 09/07/2003
 */
class ListSet[A] with Set[A] {

    def size: Int = 0;

    def contains(elem: A): Boolean = false;

    def +(elem: A): ListSet[A] = new Node(elem);

    def -(elem: A): ListSet[A] = this;

    def elements: Iterator[A] = toList.elements;

    override def toList: List[A] = Nil;

    override def equals(obj: Any): Boolean =
        if (obj.isInstanceOf[scala.collection.Set[A]]) {
            val that = obj.asInstanceOf[scala.collection.Set[A]];
            if (size != that.size) false else toList.forall(that.contains);
        } else
            false;

    override def hashCode(): Int = 0;

    protected class Node(elem: A) extends ListSet[A] {
        override def size = ListSet.this.size + 1;
        override def isEmpty: Boolean = false;
        override def contains(e: A) = (e == elem) || ListSet.this.contains(e);
        override def +(e: A): ListSet[A] = if (contains(e)) this else new Node(e);
        override def -(e: A): ListSet[A] = if (e == elem) ListSet.this else {
            val tail = ListSet.this - e; new tail.Node(elem)
        }
        override def toList: List[A] = elem :: ListSet.this.toList;
        override def hashCode(): Int = elem.hashCode() + ListSet.this.hashCode();
    }
}