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

[Rudolf Adamkovič]

That’s correct, thanks for the correction. The rule only applies to parameters with argument labels.

But still, we’d lost this guarantee of self-documenting, type-safe non-emptiness if arbitrary arrays can be passed to variadic parameters with argument labels.

R+

> On 8 Mar 2017, at 23:42, Derrick Ho <wh1pch81n at gmail.com> wrote:
> 
> Rudolf, I don't believe that is a rule.
> 
> One example includes NSLog()
> 
> In which the first parameter is a format string and the second is a variadic argument. The second one can be omitted.
> On Wed, Mar 8, 2017 at 5:09 PM Rudolf Adamkovič via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 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?
> 
> R+
> 
>> On 26 Feb 2017, at 17:26, Derrick Ho via swift-evolution <swift-evolution at swift.org <mailto: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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