[swift-evolution] [Proposal] Allow passing a variadic parameter to another variadic function

Ricardo Parada rparada at mac.com
Fri May 20 10:52:54 CDT 2016

Hi Christopher, 

Do you think something like this would work if there was a #splat() magic operator like this:

let values = [1, 2, 3, 4, 5]
let mean = arithmeticMean(#splat(values))

> On May 20, 2016, at 11:19 AM, Christopher Boyd via swift-evolution <swift-evolution at swift.org> wrote:
> Currently, Swift doesn't have a way to easily pass a variadic parameter to another variadic function because the variadic parameter itself has already been collected into an array.
> There was a prior posting a few weeks back about allowing arrays to be passed to a variadic parameter which would resolve this very specific issue:
> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160411/015185.html
> Unfortunately, that thread devolved into an argument on whether or not variadic parameters should be removed entirely.
> I, certainly, see merit in having functions that can accept a variable number of arguments and variadic functions should seem intuitive to anyone else that might be reading the code.
> Swift's documentation presents a very intuitive example:
> arithmeticMean(1, 2, 3, 4, 5)
> It's obvious what this function is doing, and any intelligent person would expect 3 as the result.  Even WolframAlpha knows how to interpret this: http://www.wolframalpha.com/input/?i=arithmeticMean(1,+2,+3,+4,+5) 
> Moreover, a function can only have ONE variadic parameter, which I think reduces any possible confusion.
> Regardless, if variadic parameters are going to stay in Swift, then I think they should at least support chaining to another function.
> The most obvious way of allowing this would be to allow variadic parameters to accept an array.
> However, I think that if an array (of the parameter type) is specified for a variadic parameter, then no other values should be allowed.  This eliminates any unnecessary complexity of potentially having to add values to the array.
> - Christopher Boyd
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