[swift-users] [Feature Request] Extend the `defer` statement

[Jun Zhang]

Hi Jay,
   I'm wrong and please ignore the "Input parameter" because I can already
get them within the defer statement body.
   Since we have a `newValue` keyword in `didSet` statement, I think a
`returnValue` keyword will be fine.

On Mon, Oct 9, 2017 at 4:49 PM, Geordie Jay <geojay at gmail.com> wrote:

> This feature request is probably one for swift evolution.
>
> I like the idea in theory, but I’d prefer to see the return value
> identifier being spelled out, i.e. “returnValue” instead of the symbols.
>
> Jun Zhang via swift-users <swift-users at swift.org> schrieb am Mo. 9. Okt.
> 2017 um 05:37:
>
>> Yes that's true, but this requires me to set a return value in every
>> `early return` statement. I think this should be done by the compiler
>> instead of me, to make code cleaner and also less error-prone.
>>
>> On Mon, Oct 9, 2017 at 11:24 AM, Slava Pestov <spestov at apple.com> wrote:
>>
>>> I think you can achieve what you want by having the ‘defer’ block
>>> capture a mutable local variable. Eg,
>>>
>>> func doStuff() {
>>>   var success = false
>>>
>>>   defer {
>>>     if !success {
>>>       // do some additional cleanup
>>>     }
>>>   }
>>>
>>>   …
>>>   success = true
>>>   …
>>>
>>>   return result
>>> }
>>>
>>> On Oct 8, 2017, at 7:34 PM, Jun Zhang via swift-users <
>>> swift-users at swift.org> wrote:
>>>
>>> Hi dear swift developers,
>>>    I am kind of new to swift and I don't know if this feature already
>>> exists. And if it exists already please tell me how. Thank you very much!
>>>   The feature is to capturing the return value (maybe input value also)
>>> of the function. Here is the demo code:
>>>
>>>     func tableView(_ tableView: UITableView, numberOfRowsInSection
>>> section: Int) -> Int {
>>>         defer {
>>>             if $> >= 0 {
>>>                 // table is not empty
>>>             }
>>>             else {
>>>                 // table is empty
>>>             }
>>>         }
>>>         return dataSource.cout
>>>     }
>>>
>>>    I suggest using `$>` as the return value symbol and `$<` as the input
>>> parameter symbol.
>>>
>>>
> Also, I’m not sure what “input parameter” means here.
>
> Geordie
>
>
>    Thank you all and best regards to you!
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>>>
>>>
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