/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2002-2010, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala
object Option
{
/** An implicit conversion that converts an option to an iterable value
*/
implicit def option2Iterable[A](xo: Option[A]): Iterable[A] = xo.toList
/** An Option factory which creates Some(value) if the argument is not null,
* and None if it is null.
*
* @param x the value
* @return Some(value) if value != null, None if value == null
*/
def apply[A](x: A): Option[A] = if (x == null) None else Some(x)
}
/** 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 1.1, 16/01/2007
*/
sealed abstract class Option[+A] extends Product {
self =>
/** True if the option is the <code>None</code> value, false otherwise.
*/
def isEmpty: Boolean
/** True if the option is a <code>Some</code>(...) false otherwise.
*/
def isDefined: Boolean = !isEmpty
/** get the value of this option.
* @note The option must be nonEmpty.
* @throws Predef.NoSuchElementException if the option is empty.
*/
def get: A
/** If the option is nonempty return its value,
* otherwise return the result of evaluating a default expression.
*
* @param default the default expression.
*/
def getOrElse[B >: A](default: => B): B =
if (isEmpty) default else this.get
/** The option's value if it is nonempty, or <code>null</code> if it is empty.
* The use of null of course is discouraged, but code written to use Options
* often must interface with code which expects and returns nulls.
*/
def orNull[A1 >: A](implicit ev: Null <:< A1): A1 = this getOrElse null
/** If the option is nonempty, return a function applied to its value,
* wrapped in a Some i.e. <code>Some(f(this.get))</code>.
* Otherwise return <code>None</code>.
*
* @param f the function to apply
*/
def map[B](f: A => B): Option[B] =
if (isEmpty) None else Some(f(this.get))
/** If the option is nonempty, return a function applied to its value.
* Otherwise return None.
* @param f the function to apply
*/
def flatMap[B](f: A => Option[B]): Option[B] =
if (isEmpty) None else f(this.get)
/** If the option is nonempty and the given predicate <code>p</code>
* yields <code>false</code> on its value, return <code>None</code>.
* Otherwise return the option value itself.
*
* @param p the predicate used for testing.
*/
def filter(p: A => Boolean): Option[A] =
if (isEmpty || p(this.get)) this else None
/** Necessary to keep Option from being implicitly converted to
* Iterable in for comprehensions.
*/
def withFilter(p: A => Boolean): WithFilter = new WithFilter(p)
/** We need a whole WithFilter class to honor the "doesn't create a new
* collection" contract even though it seems unlikely to matter much in a
* collection with max size 1.
*/
class WithFilter(p: A => Boolean) {
def map[B](f: A => B): Option[B] = self filter p map f
def flatMap[B](f: A => Option[B]): Option[B] = self filter p flatMap f
def foreach[U](f: A => U): Unit = self filter p foreach f
def withFilter(q: A => Boolean): WithFilter = new WithFilter(x => p(x) && q(x))
}
/** If the option is nonempty, p(value), otherwise false.
*
* @param p the predicate to test
*/
def exists(p: A => Boolean): Boolean =
!isEmpty && p(this.get)
/** Apply the given procedure <code>f</code> to the option's value,
* if it is nonempty. Do nothing if it is empty.
*
* @param f the procedure to apply.
*/
def foreach[U](f: A => U) {
if (!isEmpty) f(this.get)
}
/** If the given partial function <code>pf</code> is defined for the
* option's value, apply it to the value. Otherwise, None.
*
* @param pf the partial function.
*/
def collect[B](pf: PartialFunction[A, B]): Option[B] =
if (!isEmpty && pf.isDefinedAt(this.get)) Some(pf(this.get)) else None
/** If the option is nonempty return it,
* otherwise return the result of evaluating an alternative expression.
* @param alternative the alternative expression.
*/
def orElse[B >: A](alternative: => Option[B]): Option[B] =
if (isEmpty) alternative else this
/** An singleton iterator returning the option's value if it is nonempty
* or the empty iterator if the option is empty.
*/
def iterator: Iterator[A] =
if (isEmpty) Iterator.empty else Iterator.single(this.get)
/** A singleton list containing the option's value if it is nonempty
* or the empty list if the option is empty.
*/
def toList: List[A] =
if (isEmpty) List() else List(this.get)
/** An <code>Either</code> that is a <code>Left</code> with the given argument
* <code>left</code> if this is empty, or a <code>Right</code> if this is nonempty with the
* option's value.
*/
def toRight[X](left: => X) =
if (isEmpty) Left(left) else Right(this.get)
/** An <code>Either</code> that is a <code>Right</code> with the given argument
* <code>right</code> if this is empty, or a <code>Left</code> if this is nonempty with the
* option's value.
*/
def toLeft[X](right: => X) =
if (isEmpty) Right(right) else Left(this.get)
}
/** 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] {
def isEmpty = false
def get = x
}
/** This case object represents non-existent values.
*
* @author Martin Odersky
* @version 1.0, 16/07/2003
*/
case object None extends Option[Nothing] {
def isEmpty = true
def get = throw new NoSuchElementException("None.get")
}
