Scala concepts: Option Type

The 'Option' type is used to describe a computation that either has a result or does not. In Scala, you can 'chain' Option processing, combine with lists and other data structures. For example, you can also turn a pattern-match into a function that return an Option, and vice-versa!

Some examples:

assert(Option(1).flatMap(x => Option(x + 2)) == Option(3))

assert(Option(1).flatMap(x => None) == None)

final case class Page(title: String, mainCategory: Option[String])

val pages = List(
  Page(title = "Tail Recursion", mainCategory = None /** No category **/ ),
  Page(title = "Option", mainCategory = Some("standard library")),
  Page(title = "zip", mainCategory = Some("standard library"))
)

val categories: Set[String] = pages.flatMap(_.mainCategory).toSet

assert(categories == Set("standard library"))

def pageCategory(title: String): Option[String] = {
  for {
    page <- pages.find(_.title == title)
    category <- page.mainCategory
  } yield category
}

def pageCategory2(title: String): Option[String] =
  pages.find(_.title == title).flatMap(_.mainCategory)

def pageCategory3(title: String): Option[String] =
  pages.collectFirst {
    case Page(`title`, mainCategory) => mainCategory
  }.flatten

assert(pageCategory("zip").contains("standard library"))

assert(pageCategory("zip") == Some("standard library"))

assert(pageCategory("zip") == Some("standard library"))

assert(pageCategory2("zip") == pageCategory("zip"))

assert(pageCategory3("zip") == pageCategory("zip"))

assert(List[String]("X").headOption == Some("X"))

assert(List[String]().headOption.isEmpty)

val startWithT: String = Option("Some test") match {
  case Some(value) if value.startsWith("T") => value
  case Some(value)                          => s"T${value}"
  case None                                 => "T"
}

assert(startWithT == "TSome test")