Well, it kind of comes back to “tell, don’t ask”. Consider these two lines: if (opt.isDefined) println(opt.get) // versus opt foreach println In the first case, you are looking inside opt and then reacting depending on what you see. In the second case you are just telling opt what you want done, and let it … Read more
Yes, you can lift your collection to a function Int => Option[A]: scala> List(1,2,3).lift res0: Int => Option[Int] = <function1> scala> List(1,2,3).lift(9) res1: Option[Int] = None
There’s an identity function in Predef. l flatMap identity[Option[String]] > List[String] = List(Hello, World) A for expresion is nicer, I suppose: for(x <- l; y <- x) yield y Edit: I tried to figure out why the the type parameter (Option[String]) is needed. The problem seems to be the type conversion from Option[T] to Iterable[T]. … Read more
val list1 = List(Some(1), None, Some(2)) val list2 = list1.flatten // will be: List(1,2)
For comprehensions are converted into calls to the map or flatMap method. For example this one: for(x <- List(1) ; y <- List(1,2,3)) yield (x,y) becomes that: List(1).flatMap(x => List(1,2,3).map(y => (x,y))) Therefore, the first loop value (in this case, List(1)) will receive the flatMap method call. Since flatMap on a List returns another List, … Read more
The Option companion object’s apply method serves as a conversion function from nullable references: scala> Option(null) res4: Option[Null] = None scala> Option(3) res5: Option[Int] = Some(3)
If you want to get rid of the options at the same time, you can use flatten: scala> someList.flatten res0: List[String] = List(Hello, Goodbye)