fold feature (instead of matching) to simplify code / published by https://github.com/dacr/code-examples-manager #a084d3e8-7f88-4b73-9853-3448e4ea57fe/8253ab72c3a9a17d9246a8787560ef2b1fc67027

scala-feature-fold.sc

// summary : fold feature (instead of matching) to simplify code
// keywords : scala, language-feature, fold, @testable
// publish : gist
// authors : David Crosson
// license : Apache License Version 2.0 (https://www.apache.org/licenses/LICENSE-2.0.txt)
// id : a084d3e8-7f88-4b73-9853-3448e4ea57fe
// created-on : 2021-04-05T16:56:55Z
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala "3.4.2"
// ---------------------

// written after [John De Goes - 12 Steps To Better Scala (Part I)](https://youtu.be/71yhnTGw0hY)
import scala.util.{Try,Success,Failure}

// ----------------------------------------------------------------------------------------------------
{
  val input = Option("B")

  val dummy1: String = input match {
    case None => "A"
    case Some(x) => x
  }

  val dummy2: String = input.map(identity).getOrElse("A")

  val result = input.fold("A")(identity) // *** FOLD WAY WITH OPTION***

  assert(result == "B")
}
// ----------------------------------------------------------------------------------------------------
{
  val input = Option("B")

  val dummy1: Int = input match {
    case None => 1
    case Some(_) => 2
  }

  val dummy2: Int = input.map(_ => 2).getOrElse(1)

  val result: Int = input.fold(1)(_ => 2) // *** FOLD WAY WITH OPTION***

  assert(result == 2)
}
// ----------------------------------------------------------------------------------------------------

{
  val input: Either[String, String] = Right("r")

  val dummy1: Int = input match {
    case Left(_) => 1
    case Right(_) => 2
  }

  val dummy2: Int = input.toOption.map(_ => 2).getOrElse(1)

  val result: Int = input.fold(_ => 1, _ => 2) // *** FOLD WAY WITH EITHER ***

  assert(result == 2)
}

// ----------------------------------------------------------------------------------------------------
{
  val input: Try[String] = Success("something")

  val dummy1: Int = input match {
    case Failure(_) => 1
    case Success(_) => 2
  }

  val dummy2: Int = input.map(_ => 2).getOrElse(1)

  val result = input.fold(_ => 1, _ => 2) // *** FOLD WAY WITH TRY ***

  assert(result==2)
}

// ----------------------------------------------------------------------------------------------------

{
  case class UserProfile(name: String, postalCode: String)

  def getCountryFromIP(ip: String): String = "france"

  def lookupCountry(x: String) = "france"

  val someProfile = Option(UserProfile("joe", "35510"))

  // *** FOLD WAY WITH OPTION WHILE USING andThen function composition ***
  val country = someProfile.fold(getCountryFromIP("4.4.4.4"))(((x: UserProfile) => x.postalCode) andThen lookupCountry)

  assert(country == "france")
}
// ----------------------------------------------------------------------------------------------------

println("Everything OK")