[swift-evolution] Proposal for Passing Arrays to Variadic Functions

Kevin Ballard kevin at sb.org
Sat Dec 12 01:15:16 CST 2015

Using any operator at all is a problem. The only way that can work
without conflict is if the operator returns some special type that is
known to the compiler to represent a variadic call, but that doesn't
seem like a great idea. What do you think of the ... suffix? That can't
conflict with operators, and it matches the variadic function


On Fri, Dec 11, 2015, at 11:12 PM, Arthur Ariel Sabintsev wrote:
> Thanks for your response.
> The reason this doesn't work is due to Swift's generic system as it
> allows a type T to be a anything, including arrays. The example that
> was used to delineate this concept to me was that of "Any...", which
> from within the variadic function, could be interpreted as T or [T].
> The result is ambiguous in the current implementation, which is why
> some identifier syntax needs be passed along with an array to get this
> to work properly.
> As for the choice of operator, I'm open to suggestions. I wanted to
> use one that was familiar to other developers, so I chose the one that
> Ruby uses.
> Maybe a ~ would be better, or a keyword like @variadic?
> Best,
> Arthur / Sabintsev.com[1]
> On Sat, Dec 12, 2015 at 1:54 AM, Kevin Ballard via swift-evolution <swift-
> evolution at swift.org> wrote:
>> __
>> You can't use * as suggested, because that conflicts with * as a
>> prefix operator.
>> You could probably get away with using a trailing ... in the
>> call, as in
>> func foo(xs: [Int]...) {    bar(xs...) }
>> I also wonder whether there's a reason Swift doesn't already
>> support this. Maybe there's some desired future change to variadic
>> arguments to improve performance (i.e. to avoid having to allocate
>> an array) that wouldn't be compatible? Although I'm not sure what
>> that would be. Maybe there's actually no barrier at all and it was
>> just something that wasn't prioritized. It would be good to know
>> either way.
>> -Kevin
>> On Fri, Dec 11, 2015, at 10:43 PM, Arthur Sabintsev via swift-
>> evolution wrote:
>>> Hi,
>>> I have put together a proposal for passing arrays to variadic
>>> functions (along the lines of Ruby’s Splay operator).
>>> Proposal:
>>> https://github.com/ArtSabintsev/swift-evolution/blob/master/proposals/array-variadic-function.md
>>> Pull Request: https://github.com/apple/swift-evolution/pull/52 Bug
>>> Report: https://bugs.swift.org/browse/SR-128 which led to this
>>> proposal
>>> Best,
>>> Arthur / Sabintsev.com[2]
>>> _________________________________________________
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  1. http://sabintsev.com/
  2. http://sabintsev.com
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