[swift-evolution] [Idea] Passing an Array to Variadic Functions

[Sean Heber]

let myArray = Array([1, 2, 3, 4])

Is that an array with a single element that is an array, or is that a flat array with 4 numbers in it? There is no ambiguity here today - it’s an array with an array inside of it. How do you resolve this sort of situation after removing variadics?

For the record, I’m very -1 for removing variadic but very +1 for a way to inject the contents of an array into a variadic function when calling it.

l8r
Sean


> On Apr 19, 2016, at 3:06 PM, Haravikk via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> On 19 Apr 2016, at 20:25, Justin Jia <justin.jia.developer at gmail.com> wrote:
>> 
>> Cons of removing variadic functions:
>> 1. More verbose syntax. 
>> 2. Break old code. 
> 
> The verbosity is only two characters (square brackets), and it needn’t break old code:
> 
> 	Before:	func myFunc(values:Foo…)
> 	After:	func myFunc(values:[Foo])
> 
> 	Before:	myFunc(foo, bar, baz)
> 	After:	myFunc([foo, bar, baz])
> 
> Currently variadic functions just produce an array of arguments anyway, so simply translating call-sites to pass in an array guarantees compatibility.
> 
>> On Apr 19, 2016, at 10:54 AM, Haravikk <swift-evolution at haravikk.me> wrote:
>> 
>>> 
>>>> On 19 Apr 2016, at 17:51, Vladimir.S <svabox at gmail.com> wrote:
>>>> 
>>>> I.e. the question is *if we want/need to be able to pass array to existed variadic function*. Not about removing the variadic feature("removing" is offtop for this poposal, as I understand)
>>> 
>>> I’d say it’s on-topic, as removing variadic functions would eliminate the problem entirely, so if it is considered a better alternative then there would be no need to have an additional means of calling them with an array of arguments.
>>> 
>>> Personally the way I see it comes down to variadic functions is this:
>>> 
>>> Pros:
>>> 	• Slightly cleaner syntax at call-site.
>>> 	• Possibly optimisations unavailable to Array passing?
>>> 
>>> Cons:
>>> 	• Doesn’t do anything that passing an array directly can’t.
>>> 	• Passing an array is actually slightly more flexible (can dynamically pass more or less arguments as required at the call site).
>>> 	• Less explicit type at call site; gives the appearance of passing instance(s) of Foo, rather than one instance of [Foo], can lead to ambiguity with overloaded functions.
>>> 	• Extra syntax to support (enabling array passing would be more code required to support this feature)
>>> 
>>> I’d also argue that variadic functions increase the learning curve, as the first time you’re presented with one it isn’t necessarily clear what it does unless you’ve encountered them before. Like I say it can be ambiguous at the call-site in particular, as it doesn’t show that an array of [Foo] is being passed as opposed to N instances of Foo (however many are in the call).
>>> 
>>> While I’ve used them in the past, I’ve never really felt that they simplify anything enough to justify them, as it’s just two square brackets extra to pass an array; this is extra noise sure, but clarifies what is actually happening.
>>> 
>>> So if variadic functions don’t have any other advantages, then it’s really just a very minor piece of syntactic sugar that can lead to more confusion, less explicit types in function calls, an extra piece of syntax to parse and handle and possibly other features required to support it better (like the one being inquired about). The only other argument I can think of for them is that many other languages have them, but that’s not important to me vs cutting out cruft.
>>> 
>>> 
>>> Short version; removing variadic functions would solve the problem of defining overloads for both variadic and array types by only ever requiring the latter.
>>> 
>>> P.S- I’d also like to note that where possible people should be accepting Sequences or Collections in their methods anyway rather than arrays specifically, as it’s more flexible that way ;)
> 
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