Scala example source code file (SetLike.scala)

This example Scala source code file (SetLike.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

a, annotation, b, boolean, int, iterator, set, setlike, subsetsitr, that, this

The SetLike.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection

import generic._
import mutable.{ Builder, SetBuilder }
import scala.annotation.{migration, bridge}
import parallel.ParSet

/** A template trait for sets.
 *
 *  $setNote
 *  $setTags
 *  @since 2.8
 *
 *  @define setNote
 *
 *  A set is a collection that contains no duplicate elements.
 *
 *    '''Implementation note:'''
 *    This trait provides most of the operations of a `Set` independently of its representation.
 *    It is typically inherited by concrete implementations of sets.
 *
 *    To implement a concrete set, you need to provide implementations of the
 *    following methods:
 *    {{{
 *       def contains(key: A): Boolean
 *       def iterator: Iterator[A]
 *       def +(elem: A): This
 *       def -(elem: A): This
 *    }}}
 *    If you wish that methods like `take`, `drop`,
 *    `filter` return the same kind of set, you should also override:
 *    {{{
 *       def empty: This
 *    }}}
 *    It is also good idea to override methods `foreach` and
 *    `size` for efficiency.
 *
 * @define setTags
 *  @tparam A    the type of the elements of the set
 *  @tparam This the type of the set itself.
 *
 *  @author  Martin Odersky
 *  @version 2.8
 *
 *  @define coll set
 *  @define Coll Set
 *  @define willNotTerminateInf
 *  @define mayNotTerminateInf
 */
trait SetLike[A, +This <: SetLike[A, This] with Set[A]]
extends IterableLike[A, This]
   with GenSetLike[A, This]
   with Subtractable[A, This]
   with Parallelizable[A, ParSet[A]]
{
self =>

  /** The empty set of the same type as this set
   * @return  an empty set of type `This`.
   */
  def empty: This

  /** A common implementation of `newBuilder` for all sets in terms
   *  of `empty`. Overridden for mutable sets in
   *  <a href="mutable/SetLike.html" target="ContentFrame">
   *  `mutable.SetLike`</a>.
   */
  override protected[this] def newBuilder: Builder[A, This] = new SetBuilder[A, This](empty)

  protected[this] override def parCombiner = ParSet.newCombiner[A]

  /* Overridden for efficiency. */
  override def toSeq: Seq[A] = toBuffer[A]
  override def toBuffer[A1 >: A]: mutable.Buffer[A1] = {
    val result = new mutable.ArrayBuffer[A1](size)
    copyToBuffer(result)
    result
  }

  // note: this is only overridden here to add the migration annotation,
  // which I hope to turn into an Xlint style warning as the migration aspect
  // is not central to its importance.
  @migration("Set.map now returns a Set, so it will discard duplicate values.", "2.8.0")
  override def map[B, That](f: A => B)(implicit bf: CanBuildFrom[This, B, That]): That = super.map(f)(bf)

  /** Tests if some element is contained in this set.
   *
   *  @param elem the element to test for membership.
   *  @return     `true` if `elem` is contained in this set, `false` otherwise.
   */
  def contains(elem: A): Boolean

  /** Creates a new set with an additional element, unless the element is
   *  already present.
   *
   *  @param elem the element to be added
   *  @return a new set that contains all elements of this set and that also
   *          contains `elem`.
   */
  def + (elem: A): This

  /** Creates a new $coll with additional elements.
   *
   *  This method takes two or more elements to be added. Another overloaded
   *  variant of this method handles the case where a single element is added.
   *
   *  @param elem1 the first element to add.
   *  @param elem2 the second element to add.
   *  @param elems the remaining elements to add.
   *  @return   a new $coll with the given elements added.
   */
  def + (elem1: A, elem2: A, elems: A*): This = this + elem1 + elem2 ++ elems

  /** Creates a new $coll by adding all elements contained in another collection to this $coll.
   *
   *  @param elems     the collection containing the added elements.
   *  @return a new $coll with the given elements added.
   */
  def ++ (elems: GenTraversableOnce[A]): This = (repr /: elems.seq)(_ + _)

  /** Creates a new set with a given element removed from this set.
   *
   *  @param elem the element to be removed
   *  @return a new set that contains all elements of this set but that does not
   *          contain `elem`.
   */
  def - (elem: A): This

  /** Tests if this set is empty.
   *
   *  @return `true` if there is no element in the set, `false` otherwise.
   */
  override def isEmpty: Boolean = size == 0

  /** Computes the union between of set and another set.
   *
   *  @param   that  the set to form the union with.
   *  @return  a new set consisting of all elements that are in this
   *  set or in the given set `that`.
   */
  def union(that: GenSet[A]): This = this ++ that

  /** Computes the difference of this set and another set.
   *
   *  @param that the set of elements to exclude.
   *  @return     a set containing those elements of this
   *              set that are not also contained in the given set `that`.
   */
  def diff(that: GenSet[A]): This = this -- that

  /** An iterator over all subsets of this set of the given size.
   *  If the requested size is impossible, an empty iterator is returned.
   *
   *  @param len  the size of the subsets.
   *  @return     the iterator.
   */
  def subsets(len: Int): Iterator[This] = {
    if (len < 0 || len > size) Iterator.empty
    else new SubsetsItr(self.toIndexedSeq, len)
  }

  /** An iterator over all subsets of this set.
   *
   *  @return     the iterator.
   */
  def subsets: Iterator[This] = new AbstractIterator[This] {
    private val elms = self.toIndexedSeq
    private var len = 0
    private var itr: Iterator[This] = Iterator.empty

    def hasNext = len <= elms.size || itr.hasNext
    def next = {
      if (!itr.hasNext) {
        if (len > elms.size) Iterator.empty.next()
        else {
          itr = new SubsetsItr(elms, len)
          len += 1
        }
      }

      itr.next()
    }
  }

  /** An Iterator include all subsets containing exactly len elements.
   *  If the elements in 'This' type is ordered, then the subsets will also be in the same order.
   *  ListSet(1,2,3).subsets => {1},{2},{3},{1,2},{1,3},{2,3},{1,2,3}}
   *
   *  @author Eastsun
   *  @date 2010.12.6
   */
  private class SubsetsItr(elms: IndexedSeq[A], len: Int) extends AbstractIterator[This] {
    private val idxs = Array.range(0, len+1)
    private var _hasNext = true
    idxs(len) = elms.size

    def hasNext = _hasNext
    def next(): This = {
      if (!hasNext) Iterator.empty.next()

      val buf = self.newBuilder
      idxs.slice(0, len) foreach (idx => buf += elms(idx))
      val result = buf.result()

      var i = len - 1
      while (i >= 0 && idxs(i) == idxs(i+1)-1) i -= 1

      if (i < 0) _hasNext = false
      else {
        idxs(i) += 1
        for (j <- (i+1) until len)
          idxs(j) = idxs(j-1) + 1
      }

      result
    }
  }

  /** Defines the prefix of this object's `toString` representation.
   *  @return  a string representation which starts the result of `toString` applied to this set.
   *           Unless overridden this is simply `"Set"`.
   */
  override def stringPrefix: String = "Set"
  override def toString = super[IterableLike].toString

}