Scala how to pattern match for a None array

arrays, nonetype, scala

Solution

`null` isn't equals to `None`. You should wrap your array in `Option`:

Option(arr) match {
  case Some(a) => ...
  case None => ...
}

`Option(null)` returns `None`

More complete sample:

def printDoubles(arr: Array[Double]) {
    Option(arr) match {
        case Some(Array()) => println("empty array")
        case Some(a) => println(a mkString ", ")
        case None => println("array is null")
    }
}

printDoubles(null) // array is null
printDoubles(Array.empty) // empty array
printDoubles(Array(1.0, 1.1, 1.2)) // 1.0, 1.1, 1.2

Problem

For the following method, what is the way to check if the incoming array is None (aka null fro java land..) ``` val x = Array(22.0,122,222,322,422,522,622,722,822,922) def stddev(arr :Array[Double]) = { arr match { case None => 0 .. ``` The error is: ``` <console>:11: error: pattern type is incompatible with expected type; found : None.type required: Array[Double] Note: if you intended to match against the class, try `case _: <none>` case None => 0 ^ ```

Original source