Call a function with arguments from a list

Question

Is there a way to call a function with arguments from a list? The equivalent in Python is sum(*args).

// Scala

def sum(x: Int, y: Int) = x + y
val args = List(1, 4)

sum.???(args)      // equivalent to sum(1, 4)

sum(args: _*) wouldn't work here. Don't offer change the declaration of the function anyhow. I'm acquainted with a function with repeated parameters def sum(args: Int*).

Answer 1

Well, you can write

sum(args(0), args(1))

But I assume you want this to work for any list length? Then you would go for fold or reduce:

args.reduce(sum)  // args must be non empty!

(0 /: args)(sum)  // aka args.foldLeft(0)(sum)

These methods assume a pair-wise reduction of the list. For example, foldLeft[B](init: B)(fun: (B, A) => B): B reduces a list of elements of type A to a single element of type B. In this example, A = B = Int. It starts with the initial value init. Since you want to sum, the sum of an empty list would be zero. It then calls the function with the current accumulator (the running sum) and each successive element of the list.

So it's like

var result = 0
result = sum(result, 1)
result = sum(result, 4)
...

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The reduce method assumes that the list is non-empty and requires that the element type doesn't change (the function must map from two Ints to an Int).