Scala example source code file (Enumeration.scala)

This example Scala source code file (Enumeration.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

array, collection, enumeration, int, ordering, serializable, serialversionuid, string, utilities, val, value, valueset

The Enumeration.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2002-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala

import scala.collection.{ mutable, immutable, generic, SortedSetLike, AbstractSet }
import java.lang.reflect.{ Modifier, Method => JMethod, Field => JField }
import scala.reflect.NameTransformer._
import scala.util.matching.Regex

/** Defines a finite set of values specific to the enumeration. Typically
 *  these values enumerate all possible forms something can take and provide
 *  a lightweight alternative to case classes.
 *
 *  Each call to a `Value` method adds a new unique value to the enumeration.
 *  To be accessible, these values are usually defined as `val` members of
 *  the evaluation.
 *
 *  All values in an enumeration share a common, unique type defined as the
 *  `Value` type member of the enumeration (`Value` selected on the stable
 *  identifier path of the enumeration instance).
 *
 * @example {{{
 *  object Main extends App {
 *
 *    object WeekDay extends Enumeration {
 *      type WeekDay = Value
 *      val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
 *    }
 *    import WeekDay._
 *
 *    def isWorkingDay(d: WeekDay) = ! (d == Sat || d == Sun)
 *
 *    WeekDay.values filter isWorkingDay foreach println
 *  }
 *  // output:
 *  // Mon
 *  // Tue
 *  // Wed
 *  // Thu
 *  // Fri
 *  }}}
 *
 *  @param initial The initial value from which to count the integers that
 *                 identifies values at run-time.
 *  @author  Matthias Zenger
 */
@SerialVersionUID(8476000850333817230L)
abstract class Enumeration (initial: Int) extends Serializable {
  thisenum =>

  def this() = this(0)

  /* Note that `readResolve` cannot be private, since otherwise
     the JVM does not invoke it when deserializing subclasses. */
  protected def readResolve(): AnyRef = thisenum.getClass.getField(MODULE_INSTANCE_NAME).get(null)

  /** The name of this enumeration.
   */
  override def toString =
    ((getClass.getName stripSuffix MODULE_SUFFIX_STRING split '.').last split
       Regex.quote(NAME_JOIN_STRING)).last

  /** The mapping from the integer used to identify values to the actual
    * values. */
  private val vmap: mutable.Map[Int, Value] = new mutable.HashMap

  /** The cache listing all values of this enumeration. */
  @transient private var vset: ValueSet = null
  @transient @volatile private var vsetDefined = false

  /** The mapping from the integer used to identify values to their
    * names. */
  private val nmap: mutable.Map[Int, String] = new mutable.HashMap

  /** The values of this enumeration as a set.
   */
  def values: ValueSet = {
    if (!vsetDefined) {
      vset = (ValueSet.newBuilder ++= vmap.values).result()
      vsetDefined = true
    }
    vset
  }

  /** The integer to use to identify the next created value. */
  protected var nextId: Int = initial

  /** The string to use to name the next created value. */
  protected var nextName: Iterator[String] = _

  private def nextNameOrNull =
    if (nextName != null && nextName.hasNext) nextName.next() else null

  /** The highest integer amongst those used to identify values in this
    * enumeration. */
  private var topId = initial

  /** The lowest integer amongst those used to identify values in this
    * enumeration, but no higher than 0. */
  private var bottomId = if(initial < 0) initial else 0

  /** The one higher than the highest integer amongst those used to identify
    *  values in this enumeration. */
  final def maxId = topId

  /** The value of this enumeration with given id `x`
   */
  final def apply(x: Int): Value = vmap(x)

  /** Return a `Value` from this `Enumeration` whose name matches
   *  the argument `s`.  The names are determined automatically via reflection.
   *
   * @param  s an `Enumeration` name
   * @return   the `Value` of this `Enumeration` if its name matches `s`
   * @throws   NoSuchElementException if no `Value` with a matching
   *           name is in this `Enumeration`
   */
  final def withName(s: String): Value = values.find(_.toString == s).get

  /** Creates a fresh value, part of this enumeration. */
  protected final def Value: Value = Value(nextId)

  /** Creates a fresh value, part of this enumeration, identified by the
   *  integer `i`.
   *
   *  @param i An integer that identifies this value at run-time. It must be
   *           unique amongst all values of the enumeration.
   *  @return  Fresh value identified by `i`.
   */
  protected final def Value(i: Int): Value = Value(i, nextNameOrNull)

  /** Creates a fresh value, part of this enumeration, called `name`.
   *
   *  @param name A human-readable name for that value.
   *  @return  Fresh value called `name`.
   */
  protected final def Value(name: String): Value = Value(nextId, name)

  /** Creates a fresh value, part of this enumeration, called `name`
   *  and identified by the integer `i`.
   *
   * @param i    An integer that identifies this value at run-time. It must be
   *             unique amongst all values of the enumeration.
   * @param name A human-readable name for that value.
   * @return     Fresh value with the provided identifier `i` and name `name`.
   */
  protected final def Value(i: Int, name: String): Value = new Val(i, name)

  private def populateNameMap() {
    val fields = getClass.getDeclaredFields
    def isValDef(m: JMethod) = fields exists (fd => fd.getName == m.getName && fd.getType == m.getReturnType)

    // The list of possible Value methods: 0-args which return a conforming type
    val methods = getClass.getMethods filter (m => m.getParameterTypes.isEmpty &&
                                                   classOf[Value].isAssignableFrom(m.getReturnType) &&
                                                   m.getDeclaringClass != classOf[Enumeration] &&
                                                   isValDef(m))
    methods foreach { m =>
      val name = m.getName
      // invoke method to obtain actual `Value` instance
      val value = m.invoke(this).asInstanceOf[Value]
      // verify that outer points to the correct Enumeration: ticket #3616.
      if (value.outerEnum eq thisenum) {
        val id = Int.unbox(classOf[Val] getMethod "id" invoke value)
        nmap += ((id, name))
      }
    }
  }

  /* Obtains the name for the value with id `i`. If no name is cached
   * in `nmap`, it populates `nmap` using reflection.
   */
  private def nameOf(i: Int): String = synchronized { nmap.getOrElse(i, { populateNameMap() ; nmap(i) }) }

  /** The type of the enumerated values. */
  @SerialVersionUID(7091335633555234129L)
  abstract class Value extends Ordered[Value] with Serializable {
    /** the id and bit location of this enumeration value */
    def id: Int
    /** a marker so we can tell whose values belong to whom come reflective-naming time */
    private[Enumeration] val outerEnum = thisenum

    override def compare(that: Value): Int =
      if (this.id < that.id) -1
      else if (this.id == that.id) 0
      else 1
    override def equals(other: Any) = other match {
      case that: Enumeration#Value  => (outerEnum eq that.outerEnum) && (id == that.id)
      case _                        => false
    }
    override def hashCode: Int = id.##

    /** Create a ValueSet which contains this value and another one */
    def + (v: Value) = ValueSet(this, v)
  }

  /** A class implementing the [[scala.Enumeration.Value]] type. This class
   *  can be overridden to change the enumeration's naming and integer
   *  identification behaviour.
   */
  @SerialVersionUID(0 - 3501153230598116017L)
  protected class Val(i: Int, name: String) extends Value with Serializable {
    def this(i: Int)       = this(i, nextNameOrNull)
    def this(name: String) = this(nextId, name)
    def this()             = this(nextId)

    assert(!vmap.isDefinedAt(i), "Duplicate id: " + i)
    vmap(i) = this
    vsetDefined = false
    nextId = i + 1
    if (nextId > topId) topId = nextId
    if (i < bottomId) bottomId = i
    def id = i
    override def toString() =
      if (name != null) name
      else try thisenum.nameOf(i)
      catch { case _: NoSuchElementException => "<Invalid enum: no field for #" + i + ">" }

    protected def readResolve(): AnyRef = {
      val enum = thisenum.readResolve().asInstanceOf[Enumeration]
      if (enum.vmap == null) this
      else enum.vmap(i)
    }
  }

  /** An ordering by id for values of this set */
  object ValueOrdering extends Ordering[Value] {
    def compare(x: Value, y: Value): Int = x compare y
  }

  /** A class for sets of values.
   *  Iterating through this set will yield values in increasing order of their ids.
   *
   *  @param nnIds The set of ids of values (adjusted so that the lowest value does
   *    not fall below zero), organized as a `BitSet`.
   */
  class ValueSet private[ValueSet] (private[this] var nnIds: immutable.BitSet)
  extends AbstractSet[Value]
     with immutable.SortedSet[Value]
     with SortedSetLike[Value, ValueSet]
     with Serializable {

    implicit def ordering: Ordering[Value] = ValueOrdering
    def rangeImpl(from: Option[Value], until: Option[Value]): ValueSet =
      new ValueSet(nnIds.rangeImpl(from.map(_.id - bottomId), until.map(_.id - bottomId)))

    override def empty = ValueSet.empty
    def contains(v: Value) = nnIds contains (v.id - bottomId)
    def + (value: Value) = new ValueSet(nnIds + (value.id - bottomId))
    def - (value: Value) = new ValueSet(nnIds - (value.id - bottomId))
    def iterator = nnIds.iterator map (id => thisenum.apply(bottomId + id))
    override def keysIteratorFrom(start: Value) = nnIds keysIteratorFrom start.id  map (id => thisenum.apply(bottomId + id))
    override def stringPrefix = thisenum + ".ValueSet"
    /** Creates a bit mask for the zero-adjusted ids in this set as a
     *  new array of longs */
    def toBitMask: Array[Long] = nnIds.toBitMask
  }

  /** A factory object for value sets */
  object ValueSet {
    import generic.CanBuildFrom

    /** The empty value set */
    val empty = new ValueSet(immutable.BitSet.empty)
    /** A value set consisting of given elements */
    def apply(elems: Value*): ValueSet = (newBuilder ++= elems).result()
    /** A value set containing all the values for the zero-adjusted ids
     *  corresponding to the bits in an array */
    def fromBitMask(elems: Array[Long]): ValueSet = new ValueSet(immutable.BitSet.fromBitMask(elems))
    /** A builder object for value sets */
    def newBuilder: mutable.Builder[Value, ValueSet] = new mutable.Builder[Value, ValueSet] {
      private[this] val b = new mutable.BitSet
      def += (x: Value) = { b += (x.id - bottomId); this }
      def clear() = b.clear()
      def result() = new ValueSet(b.toImmutable)
    }
    /** The implicit builder for value sets */
    implicit def canBuildFrom: CanBuildFrom[ValueSet, Value, ValueSet] =
      new CanBuildFrom[ValueSet, Value, ValueSet] {
        def apply(from: ValueSet) = newBuilder
        def apply() = newBuilder
      }
  }
}