Difference between Int... and Int[]

Question

Why does the following fail to compile (getting this for an error: Could not find an overload for '_conversion' that accepts the supplied arguments) when passing in a Int...?

func sumOfNumbers(numbers: Int...) -> Int{
    var sum = 0;
    for number in numbers{
        sum += number
    }
    return sum
}

func averageOfInts(numbers: Int...) -> Int{
    var sumNums: Int = 0
    sumNums = sumOfNumbers(numbers)
    var count = numbers.count
    return sumOfNumbers(numbers)/numbers.count
}

But when a Int[] is used in place of the Int... it compiles and works as expected.

Answer 1

When the type of an argument is Int... all the subsequent args are bunched into the array for you, whereas Int[] requires you to pass just one argument, an array of Ints:

func sumOfIntsSplat(numbers:Int...) -> Int {
    var sum = 0;
    for number in numbers{
        sum += number
    }
    return sum
}
func sumOfIntsArray(numbers: Int[]) -> Int{
    var sum = 0;
    for number in numbers{
        sum += number
    }
    return sum
}

Usage

sumOfIntsSplat(1,2,3,4,5)
sumOfIntsArray([1,2,3,4,5])

The Int... syntax is referred to as a Variadic parameter in the swift documentation

(aside: I borrowed the name "splat" from coffeescript, where I first encountered this syntax)