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Scala example source code file (Set.scala)

This example Scala source code file (Set.scala) is included in the "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Scala by Example" TM.

Learn more about this Scala project at its project page.

Java - Scala tags/keywords

arraystack, boolean, foldable, isempty, monoid, order, set, setfunctions, setinstances, show

The Set.scala Scala example source code

package scalaz
package std

trait SetInstances {
  implicit val setInstance: Foldable[Set] with IsEmpty[Set] = new Foldable[Set] with IsEmpty[Set] with Foldable.FromFoldr[Set] {
    override def length[A](fa: Set[A]) = fa.size
    def empty[A] = Set()
    def plus[A](a: Set[A], b: => Set[A]) = a ++ b
    def isEmpty[A](fa: Set[A]) = fa.isEmpty

    override def toSet[A](fa: Set[A]) = fa

    def foldRight[A, B](fa: Set[A], z: => B)(f: (A, => B) => B) = {
      import scala.collection.mutable.ArrayStack
      val s = new ArrayStack[A]
      fa.foreach(a => s += a)
      var r = z
      while (!s.isEmpty) {
        // Fixes stack overflow issue (#866)
        val w = r
        r = f(s.pop, w)
    override def all[A](fa: Set[A])(f: A => Boolean) =
      fa forall f
    override def any[A](fa: Set[A])(f: A => Boolean) =
      fa exists f

  import Ordering._

   * We could derive set equality from `Equal[A]`, but it would be `O(n^2)`.
   * Instead, we require `Order[A]`, reducing the complexity to `O(log n)`
   * If `Equal[A].equalIsNatural == true`, than `Any#==` is used.
  implicit def setOrder[A: Order]: Order[Set[A]] = new Order[Set[A]] {
    def order(a1: Set[A], a2: Set[A]) = {
      import anyVal._
      import scala.math.Ordering.Implicits._
      implicit val o = Order[A].toScalaOrdering
      implicit val so = Order.fromScalaOrdering(seqDerivedOrdering[Seq, A])
      Order[Int].order(a1.size, a2.size) match {
        case EQ => Order.orderBy((s: Set[A]) => s.toSeq.sorted).order(a1, a2)
        case x => x

    override def equal(a1: Set[A], a2: Set[A]) = {
      if (equalIsNatural) a1 == a2
      else {
        implicit val x = Order[A].toScalaOrdering
        import scala.collection.immutable.TreeSet
        val s1 = TreeSet[A](a1.toSeq: _*)
        val s2 = TreeSet[A](a2.toSeq: _*)
    override val equalIsNatural: Boolean = Equal[A].equalIsNatural

  implicit def setMonoid[A]: Monoid[Set[A]] = new Monoid[Set[A]] {
    def append(f1: Set[A], f2: => Set[A]) = f1 ++ f2
    def zero: Set[A] = Set[A]()

  implicit def setShow[A: Show]: Show[Set[A]] = new Show[Set[A]] {
    override def show(as: Set[A]) = Cord("Set(", Cord.mkCord(",",[A].show).toSeq:_*), ")")


trait SetFunctions

object set extends SetInstances with SetFunctions

Other Scala examples (source code examples)

Here is a short list of links related to this Scala Set.scala source code file:

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