[swift-evolution] [Pitch] Replace 'inout' with '&'

[Dmitri Gribenko]

On Mon, Dec 21, 2015 at 10:40 AM, Matthew Johnson
<matthew at anandabits.com> wrote:
>
>> On Dec 21, 2015, at 12:36 PM, Dmitri Gribenko via swift-evolution <swift-evolution at swift.org> wrote:
>>
>> On Mon, Dec 21, 2015 at 10:34 AM, Joe Groff <jgroff at apple.com> wrote:
>>>
>>>> On Dec 18, 2015, at 6:52 PM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
>>>>
>>>> On Fri, Dec 18, 2015 at 6:21 PM, Joe Groff <jgroff at apple.com> wrote:
>>>>>
>>>>> On Dec 18, 2015, at 6:08 PM, Dmitri Gribenko <gribozavr at gmail.com> wrote:
>>>>> There's also a possibility that we add 'out' parameters in the future, and
>>>>> if 'inout' would be spelled '&', then we would need to find another sigil
>>>>> for 'out'.
>>>>>
>>>>> We have multiple returns. Why would we ever add out parameters?
>>>>
>>>> I don't want to turn this thread into a discussion about out
>>>> parameters, but one reason would be to replace
>>>> AutoreleasingUnsafeMutablePointer.
>>>
>>> IMO we should eventually import out params from C as multiple returns.
>>>
>>>> Another one is to add labels to
>>>> the output parameters:
>>>>
>>>> let (day, month, year) = parseDate()
>>>> let (year, day, month) = parseDate() // bug?
>>>
>>> Labeled tuples seem like they could help with that, with compiler QoI to catch cases like this where you obviously permuted the return names.
>>
>> Currently they don't help:
>>
>> (swift) func parseDate() -> (day: Int, month: Int, year: Int) { return (0,0,0) }
>> (swift) let (year, month, day) = parseDate()
>> // (year, month, day) : (Int, Int, Int) = (0, 0, 0)
>
>
> Looks like they help to me:
>
> func labeledMultiReturn() -> (string: String, int: Int) {
>     return (string: "hello", int: 42)
> }
>
> let (string: boundString, int: boundInt) = labeledMultiReturn()
>
> print(boundString)
> print(boundInt)

Well, they don't *force* you to use labels at the use site,
allowing bugs to happen even if the API author went out of their way
and used labels.

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/