使用asInstanceOf将Any转换为Double

Question

I have a function that takes a variable number of arguments. The first is a String and the rest are numbers (either Int or Double) so I am using Any* to get the arguments. I would like to treat the numbers uniformly as Doubles, but I cannot just use asInstanceOf[Double] on the numeric arguments. For example:

 val arr = Array("varargs list of numbers", 3, 4.2, 5)
 val d = arr(1).asInstanceOf[Double]

gives:

 java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Double

Is there a way to do this? (The function needs to add up all the numbers).

Answer 1

Scala's asInstanceOf is its name for casting. Casting is not converting.

What you want can be accomplished like this:

val mongrel = List("comment", 1, 4.0f, 9.00d)
val nums = mongrel collect { case i: Int => i case f: Float => f case d: Double => d }
val sumOfNums = nums.foldLeft(0.0) ((sum, num) => sum + num)

Answer 2

Here is a slight simplification of Randall's answer:

val mongrel = List("comment", 1, 4.0f, 9.00d)
val nums = mongrel collect { case i: java.lang.Number => i.doubleValue() }
val sumOfNums = nums.sum

Matching for any kind of number turns out to be a little tricky in Scala, see here for another way of doing it.

Answer 3

When there is a need to handle different types, you should avoid casting them and instead use a pattern match. To add up all Double's and Int's of an array you could use:

val array = Array("varargs list of numbers", 3, 4.2, 5)

array.foldLeft(0.0){ 
  case (s, i: Int) => s + i
  case (s, d: Double) => s + d
  case (s, _) => s
}

The pattern match allows you to treat each different type separately and avoids running into ClassCastExceptions .

Answer 4

Stepping back for a moment, might it be easier to have the function take Double* instead of Any* ?

scala> def foo(str: String, nums: Double*) { 
    nums foreach { n => println(s"num: $n, class:   ${n.getClass}") } 
}
foo: (str: String, nums: Double*)Unit

scala> foo("", 1, 2.3)
num: 1.0, class: double
num: 2.3, class: double