Subtracting two Option[Double]-CodePudding

I have two variables that are optional double and I want to consider them as 0 when they are None

var x: Option[Double] = Option(0)
var y: Option[Double] = Option(0)
println("Expected 0 : " (x    y).reduceOption(_ - _)) // 0

x = Option(4)
y = Option(0)
println("Expected 4 : " (x    y).reduceOption(_ - _)) // 4

x = Option(0)
y = Option(4)
println("Expected -4 : " (x    y).reduceOption(_ - _)) // -4

x = Option(4)
y = None
println("Expected 4 : " (x    y).reduceOption(_ - _)) // 4

x = None
y = Option(4.0)
println("Expected -4 : " (x    y).reduceOption(_ - _)) // 4

The last one I am expecting -4 but I get 4.

If I use

(for (i <- x; j <- y) yield i - j)

then I get None.

Also If I try

x.getOrElse(0) - y.getOrElse(0) // value - is not a member of AnyVal

then I get error value - is not a member of AnyVal

CodePudding user response：

The (x y).reduceOption(_ - _) is a perfect example of how to confuse people in Scala IMHO. It's not immediate that operates on Option because they are also Seq.

That being said, as already suggested in the comments, the straightforward way would be to use getOrElse:

x.getOrElse(0d) - y.getOrElse(0d)

You need to precise the d to have an Double otherwise, you get an AnyVal because AnyVal is the only common parent type of Int (from the getOrElse) and Double (value in the option).