How do I pull apart Case Classes filled with Options in Scala

Question

I'm very new to Scala and I'm still trying to get used to the syntax and style, so this is probably a very simple question.

I'm working with a codebase where there are lots of case classes populated with Options like so:

case class Person(
  pants: Option[Pants]
)
case class Pants(
  pocket: Option[Pocket]
)
case class Pocket(
  cash: Option[Cash]
)
case class Cash(
  value: String = "zilch"
)

In the example above, how would you go about returning how much money is in a Person's Pants Pocket, if they are indeed wearing pants... with pockets, and if they have any money at all?

Answer 1

Scalaz 7 has changed a little so here is another example:

  object PartialLensExample extends App {

  import scalaz._
  import Lens._
  import PLens._


  case class Bar(blub: Option[String])
  case class Foo(bar: Option[Bar])

  // normal lenses for getting and setting values
  val fooBarL: Foo @> Option[Bar] = lensg(foo ⇒ bar ⇒ foo.copy(bar = bar), _.bar)
  val barBlubL: Bar @> Option[String] = lensg(bar ⇒ blub ⇒ bar.copy(blub = blub), _.blub)

  // compose the above as 'Partial Lenses', >=> is just an alias for 'andThen'
  val fooBarBlubL: Foo @?> String = fooBarL.partial >=> somePLens >=> barBlubL.partial >=> somePLens

  // try it
  val foo = Foo(Some(Bar(Some("Hi"))))

  println(fooBarBlubL.get(foo)) // Some(Hi)

  println(fooBarBlubL.set(foo, "Bye")) //Foo(Some(Bar(Some(Bye))))

  // setting values
  val foo2 = Foo(None)
  println(fooBarL.set(foo2, Some(Bar(None)))) // Foo(Some(Bar(None)))

}

Answer 2

A great time for for-comprehensions:

val someCash: Option[Cash] =
   for( pants  <- somePerson.pants;
        pocket <- pants.pocket;
        cash   <- pocket.cash ) yield cash

Equivalently you can write the following, for which the first code is syntactic sugar (ignoring some subtleties):

val someCash: Option[Cash] = 
   somePerson.pants.flatMap(_.pocket.flatMap(_.cash))

(I'm not totally sure if you can write the last expression using the _ wildcards, as I did).