[swift-evolution] [pitch] Variadic Arguments should accept Arrays

Rudolf Adamkovič salutis at me.com
Wed Mar 8 16:09:27 CST 2017

Correct me if I’m wrong but a variadic argument is guaranteed to have one or more elements in the array. Isn’t that the case? As an example, consider the following initializer:

    public init(state: State, actions: Action...) {
        // ...

Here, I can count on actions to be a non-empty array. It’s self-documenting and type-safe. How would this work if arrays are (implicitly or explicitly) convertible to variadic arguments?


> On 26 Feb 2017, at 17:26, Derrick Ho via swift-evolution <swift-evolution at swift.org> wrote:
> In swift, a variadic argument can become an array without too much effort.
> func foo(_ va: String...) {
>    let a: [String] = va
> }
> However, it seems odd to me that an array can not be converted into a variadic argument
> foo(["a", "b", "c"]) // <-error
> foo("a", "b", "c") // no error
> Other people have wondered about this too. <http://stackoverflow.com/questions/24024376/passing-an-array-to-a-function-with-variable-number-of-args-in-swift>
> According to this thread <https://devforums.apple.com/message/970958#970958> Doug Gregor says it is due to some type ambiguity. with Generics.
> If type ambiguity is the issue, Do we have the option to cast it to the correct type?
> foo(["a", "b", "c"] as String...) // <- error.  doesn't consider String... to be a type.
> What does the community think? Should we be granted some mechanism to turn an array into a variadic argument?
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