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package spire
package util

import spire.algebra.Eq
import spire.syntax.eq._

object Opt extends OptVersions {
  def apply[A](a: A): Opt[A] = new Opt(a)
  def empty[A]: Opt[A] = new Opt[A](null.asInstanceOf[A])

  implicit def Eq[A: Eq]: Eq[Opt[A]] = new Eq[Opt[A]] {
    def eqv(x: Opt[A], y: Opt[A]): Boolean =
      if (x.isEmpty) y.isEmpty else x.ref === y.ref
  }
}

class Opt[+A](val ref: A) extends OptVersions.Base {
  def scala2_10hashCode: Int = ref.hashCode
  def scala2_10equals(other: Any): Boolean = other match {
    case that: Opt[_] => ref == that.ref
    case _ => false
  }
  def isDefined: Boolean = ref != null
  def nonEmpty: Boolean = ref != null
  def isEmpty: Boolean = ref == null

  def get: A = if (ref == null) throw new NoSuchElementException("Opt.empty.get") else ref

  override def toString: String =
    if (ref == null) "Opt.empty" else s"Opt($ref)"

  def filter(f: A => Boolean): Opt[A] =
    if (ref != null && f(ref)) this else Opt.empty

  def map[B](f: A => B): Opt[B] =
    if (ref == null) Opt.empty else Opt(f(ref))

  def flatMap[B](f: A => Opt[B]): Opt[B] =
    if (ref == null) Opt.empty else f(ref)

  def fold[B](b: => B)(f: A => B): B =
    if (ref == null) b else f(ref)


  def getOrElse[B >: A](default: => B): B = if (ref == null) default else ref

  def getOrElseFast[B >: A](default: B): B = if (ref == null) default else ref

  def toOption: Option[A] = if (ref == null) None else Some(ref)

  def toList: List[A] = if (ref == null) Nil else (ref :: Nil)

  def contains[A1 >: A](elem: A1): Boolean = if (ref == null) false else ref == elem

  def exists(p: A => Boolean): Boolean = if (ref == null) false else p(ref)

  def forall(p: A => Boolean): Boolean = if (ref == null) true else p(ref)

  def foreach[U](f: A => U): Unit = if (ref != null) f(ref)

  def iterator: Iterator[A] = if (ref == null) collection.Iterator.empty else collection.Iterator.single(ref)

  def toRight[X](left: => X): Either[X, A] =
    if (ref == null) Left(left) else Right(ref)

  def toLeft[X](right: => X): Either[A, X] =
    if (ref == null) Right(right) else Left(ref)
}