for-comprehension.sc

case class Meal(
  starter: Option[String],
  main: String,
  drinks: Seq[String],
  tip: Option[Int]
)

val meals = Seq(
  Meal(
    starter = Some("Zucchini Fritters"),
    main = "Ravioli",
    drinks = Seq("Mojito", "Wine"),
    tip = Some(5)
  ),
  Meal(
    starter = Some("Papa Qashqai"),
    main = "Salad",
    drinks = Seq("Water", "Coffee"),
    tip = None
  )
)



def describeStarterAndTipCombo(meal: Meal): Option[String] = for {
  starter <- meal.starter // this is an Option[_], so all the other generators must be Option[_] too
  tip <- meal.tip
} yield s"The $starter came so quick, our tip was $tip"

describeStarterAndTipCombo(meals.head)



def allTheDrinksFrom(meals: Seq[Meal]): Seq[String] = for {
  meal <- meals
  drink <- meal.drinks // this is a Seq[_] too, so everything's ok!
} yield drink

allTheDrinksFrom(meals)



def allTipsFrom(meals: Seq[Meal]): Seq[Int] = for {
  meal <- meals
  tip <- meal.tip // this works, because Seq[_] has a .flatMap that accepts IterableOnce[_], which Option[_] is
} yield tip

allTipsFrom(meals)



def describeAllStarterAndDrinksCombo(meal: Meal) = for {
  starter <- meal.starter // this is an Option[_], so the other generators must be Option[_] too
  drink <- meal.drinks // we'll get a compile error here
} yield s"$starter with $drink"

describeAllStarterAndDrinksCombo(meals(0))