[swift-evolution] array splatting for variadic parameters

Dimitri Racordon Dimitri.Racordon at unige.ch
Thu Feb 9 17:51:28 CST 2017

Hello everyone.

I understand that topic has already been discussed in the past, but I failed to get any information on its current state of affairs.

I guess the subject of this mail is explicit, but to make sure I’m clear, here's a small snippet that illustrates the problem:

func f(args: Int…) {
  // Some implementation ...
// Now it's impossible to call f without explicitly naming its parameters.

For many use-cases, this problem can be solved by overloading f so that it explicitly accepts an array.

func f(_ args: [Int]) {
  // Some implementation ...

func f(_ args: Int…) {

Some people also advocate (myself generally included) that one should prefer the signature explicitly marking args as an array, as the syntactic overhead of wrapping the arguments with “[]” when calling f is arguably bearable. However, in some other situations, this approach might not be applicable. For instance, one may simply not be able to modify the original function. Another use-case may be a function that should forward its own variadic parameters.

In a variety of other languages, there exists a way to do this. For instance, Python can “unpack” (or splat) a list into function arguments by prefixing it with *:

def f(*args):
  # Some implementation …

f(*[1, 2, 3]) # == f(1, 2, 3)

I was wondering if such feature could be supported by Swift, and if not, why.

Syntactically, I like the use of “…”, which would mirror function signatures:

f(…[1, 2, 3]) // == f(1, 2, 3)


Dimitri Racordon

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