Function taking a variable number of arguments

Question

In this document: https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GuidedTour.html#//apple_ref/doc/uid/TP40014097-CH2-XID_1

It mentions that when creating for loops we can use the shorthand of 0..3 and 0...3 to replace i = 0; i < 3; ++i and i = 0; i <= 3; ++i respectively.

All very nice.

Further down the document in the Functions and Closures section it says that functions can have a variable number of arguments passed via an array.

However, in the code example we see the ... again.

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

Is this a mistake? It seems to me that a more intuitive syntax would be numbers: Int[].

A few examples down we see another code sample which has exactly that:

func hasAnyMatches(list: Int[], condition: Int -> Bool) -> Bool {

Answer 1

In case of all arguments are Int numbers: Int[] would be intuitive. But if you have code like this:

func foo(args:AnyObject...) {
    for arg: AnyObject in args {
        println(arg)
    }
}

foo(5, "bar", NSView())

output:

5
bar
<NSView: 0x7fc5c1f0b450>

Answer 2

The type of parameter in sumOf are known as 'variadic' parameter. The parameters passed are accepted just as a group of elements and is then converted into array before using it within that function.

A great example would be this post.

Passing lists from one function to another in Swift