Question

In scala, how do I define addition over two Option arguments? Just to be specific, let’s say they’re wrappers for Int types (I’m actually working with maps of doubles but this example is simpler).

I tried the following but it just gives me an error:

  def addOpt(a:Option[Int], b:Option[Int]) = {
    a match {
      case Some(x) => x.get
      case None => 0
    } + b match {
      case Some(y) => y.get
      case None => 0
    }
  }

Edited to add:

In my actual problem, I’m adding two maps which are standins for sparse vectors. So the None case returns Map[Int, Double] and the + is actually a ++ (with the tweak at stackoverflow.com/a/7080321/614684)

Answer 1

(Repeating comment above in an answer as requested)

You don’t extract the content of the option the proper way. When you match with case Some(x), x is the value inside the option(type Int) and you don’t call get on that. Just do

case Some(x) => x 

Anyway, if you want content or default, a.getOrElse(0) is more convenient