Question

I have a List[Option[MyClass]] with None in random positions and I need to ‘fill’ that list again, from a List[MyClass], maintaining the order.

Here are sample lists and expected result:

val listA = List(Some(3),None,Some(5),None,None)
val listB = List(7,8,9)
val expectedList = List(Some(3), Some(7), Some(5), Some(8), Some(9))

So, how would be a idiomatic Scala to process that list?

Answer 1

def fillL[T](a:List[Option[T]], b:List[T]) = {
    val iterB = b.iterator
    a.map(_.orElse(Some(iterB.next)))
}