path: root/src/library/scala/Option.scala

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2002-2006, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |                                         **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

// $Id$


package scala;

import Predef._

/** This class represents optional values. Instances of <code>Option</code>
 *  are either instances of case class <code>Some</code> or it is case
 *  object <code>None</code>.
 *
 *  @author  Martin Odersky
 *  @author  Matthias Zenger
 *  @version 1.0, 16/07/2003
 */
sealed abstract class Option[+A] extends Iterable[A] with CaseClass {

  def isEmpty: Boolean = this match {
    case None => true
    case _ => false
  }

  def get: A = this match {
    case None => Predef.error("None.get")
    case Some(x) => x
  }

  def get[B >: A](default: B): B = this match {
    case None => default
    case Some(x) => x
  }

  def map[B](f: A => B): Option[B] = this match {
    case None => None
    case Some(x) => Some(f(x))
  }

  def flatMap[B](f: A => Option[B]): Option[B] = this match {
    case None => None
    case Some(x) => f(x)
  }

  def filter(p: A => Boolean): Option[A] = this match {
    case None => None
    case Some(x) => if (p(x)) Some(x) else None
  }

  override def foreach(f: A => Unit): Unit = this match {
    case None => ()
    case Some(x) => f(x)
  }

  def elements: Iterator[A] = this match {
    case None => Iterator.empty
    case Some(x) => Iterator.fromValues(x)
  }

  override def toList: List[A] = this match {
    case None => List()
    case Some(x) => List(x)
  }

}

/** Class <code>Some[A]</code> represents existing values of type
 *  <code>A</code>.
 *
 *  @author  Martin Odersky
 *  @version 1.0, 16/07/2003
 */
final case class Some[+A](x: A) extends Option[A];

/** This case object represents non-existent values.
 *
 *  @author  Martin Odersky
 *  @version 1.0, 16/07/2003
 */
case object None extends Option[Nothing];