Exc10 Scala Option

[dominik_andreas]

Can somebody explain to me why Scala Option is being used (ie in store.get) instead of just returning the actual value? Whats the point of using Scala Option in general?

[Osterlaus]

http://blog.danielwellman.com/2008/03/u ... as-op.html can give you a first insight about this.

[dominik_andreas]

Thats what i suspected, but the article was a great starting point for a lot more insight. Thanks!

[yourmaninamsterdam]

Note that the Option type implements map and foreach that are executed only if the Option is-a Some. Using that, you can get rid of a lot if if-else/match code. Also, if you have Lists of Option, you can use flatten to remove all appearances of None and get all Somes.

Here are the examples:

Code: Alles auswählen

scala> val some = Some(3)
some: Some[Int] = Some(3)

scala> val none: Option[Int] = None
none: Option[Int] = None

scala> some.foreach(println)
3

scala> none.foreach(println)

scala> some.map(_ * math.Pi)
res2: Option[Double] = Some(9.42477796076938)

scala> none.map(_ * math.Pi)
res3: Option[Double] = None

scala> none.map(_ * math.Pi).getOrElse(1)
res4: AnyVal = 1

scala> List(Some(1), Some(2), None, Some(4)).flatten
res5: List[Int] = List(1, 2, 4)

As you see at the val definition, a light "pitfall" is that the type inference is quite tight. If you initialize a variable with None, it will not infer Option[YourType], but None, because your type cannot be infered from the context; you will have to declare it explicitely.