[swift-evolution] [Pitch] Tuple Destructuring in Parameter Lists

[Dennis Weissmann]

Hi Brent,

Thanks! Those are great points!

I haven’t thought about the possibility of suppressing the external label. I like your option 2 very much! I’ll add it to the proposal and change the used variable names. 

- Dennis

> On May 30, 2016, at 3:01 PM, Brent Royal-Gordon <brent at architechies.com> wrote:
> 
>> // Allowed today:
>> func takesATuple(tuple: (Int, Int)) {
>>  let valueA = tuple.0
>>  let valueB = tuple.1
>>  // ...
>> }
>> 
>> // Proposed syntax:
>> func takesATuple(tuple (valueA, valueB): (Int, Int)) {
>>  // use valueA
>>  // use valueB
>> }
> 
> Personally, I find this example confusing because the label is "tuple", which kind of reads like a keyword, and because you're using the same name for the label and variable. If I understand the semantics you're proposing correctly, I think it would be clearer to write this example like:
> 
> // Allowed today:
> func takes(a tuple: (Int, Int)) {
>  let valueA = tuple.0
>  let valueB = tuple.1
>  // ...
> }
> 
> // Proposed syntax:
> func takes(a (valueA, valueB): (Int, Int)) {
>  // use valueA
>  // use valueB
> }
> 
> Incidentally, it may also be a good idea to define what happens if you write:
> 
> func takes((valueA, valueB): (Int, Int))
> 
> Normally, if there's no separate label and variable name, they're the same, but you can't have a label like `(valueA, valueB)`. I see two reasonably sensible answers here:
> 
> 1. It's equivalent to writing `_ (valueA, valueB)`.
> 2. It's illegal. You have to write a label, or `_` if you don't want one.
> 
> My preference would be for #2, but you're the designer, not me.
> 
> -- 
> Brent Royal-Gordon
> Architechies
> 

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