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