Option.scala

/*
 * Copyright (c) 2014-2019 Israel Herraiz <isra@herraiz.org>
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */  

// --------------------------------------
// Option type for exercises in chapter 4
// --------------------------------------

package errorhandling

// Hide real Scala Option and Either
import scala.{Option => _, Either => _, _}

sealed trait Option[+A] {

  def map[B](f: A => B): Option[B] = {
    this match {
      case None => None
      case Some(x) => Some(f(x))
    }
  }

  def getOrElse[B >: A](default: => B): B = {
    this match {
      case Some(x) => x
      case None => default
    }
  }

  def flatMap[B](f: A => Option[B]): Option[B] = {
    map(f).getOrElse(None)
  }

  def orElse[B >: A](ob: => Option[B]): Option[B] = {
    this.map(Some(_)).getOrElse(ob)
  }

  def filter(f: A => Boolean): Option[A] = {
    this.flatMap(x => if (f(x)) Some(x) else None)
  }

}
case class Some[+A](get: A) extends Option[A]
case object None extends Option[Nothing]