[swift-evolution] Required Callback

[Xiaodi Wu]

One alternative that comes to mind:

The @escaping stuff came with a helper function, withoutActuallyEscaping,
to deal with attribute mismatches. Perhaps we could have the same here, for
consistency, something like withActuallyInvoking?
On Tue, Aug 16, 2016 at 12:05 Xiaodi Wu <xiaodi.wu at gmail.com> wrote:

> Well, the callsite @required would be what I call your escape hatch :)
>
> Hmm, lemme think on this...
> On Tue, Aug 16, 2016 at 11:59 James Campbell <james at supmenow.com> wrote:
>
>> It would though, look :) :
>>
>> Backend.run() { requiredCallback in
>>
>>  NonAnotatedModuled({
>>
>> //We send a anon closure to the module and we call the callback with a
>> required specifier to indicate to the compiler it will be called :)
>> @required requiredCallback()
>> })
>> }
>>
>> This would be the same as this:
>>
>>
>> Backend.run() { requiredCallback in
>>
>>  AnotatedModuled(requiredCallback)
>> }
>>
>> And this:
>>
>>
>> Backend.run() { requiredCallback in
>>
>> @required requiredCallback()
>> }
>>
>> *___________________________________*
>>
>> *James⎥Lead Hustler*
>>
>> *james at supmenow.com <james at supmenow.com>⎥supmenow.com
>> <http://supmenow.com>*
>>
>> *Sup*
>>
>> *Runway East *
>>
>> *10 Finsbury Square*
>>
>> *London*
>>
>> * EC2A 1AF *
>>
>> On 16 August 2016 at 17:55, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>>
>>> Wait, doesn't work. Your anonymous closure would then be dinged for not
>>> satisfying the requirement. Turtles all the way down. Still need an escape
>>> hatch.
>>>
>>> On Tue, Aug 16, 2016 at 11:54 James Campbell <james at supmenow.com> wrote:
>>>
>>>> I'll write up a draft proposal :) I think we have something nice :)
>>>>
>>>> *___________________________________*
>>>>
>>>> *James⎥Lead Hustler*
>>>>
>>>> *james at supmenow.com <james at supmenow.com>⎥supmenow.com
>>>> <http://supmenow.com>*
>>>>
>>>> *Sup*
>>>>
>>>> *Runway East *
>>>>
>>>> *10 Finsbury Square*
>>>>
>>>> *London*
>>>>
>>>> * EC2A 1AF *
>>>>
>>>> On 16 August 2016 at 17:54, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>>>>
>>>>> Nicer still!
>>>>>
>>>>> On Tue, Aug 16, 2016 at 11:53 James Campbell <james at supmenow.com>
>>>>> wrote:
>>>>>
>>>>>> I guess that would make sense and you could wrap the callback up in a
>>>>>> anon-closure if the module hadn't adpated the @required property so you get
>>>>>> both compatibility, safety and clarity.
>>>>>>
>>>>>> *___________________________________*
>>>>>>
>>>>>> *James⎥Lead Hustler*
>>>>>>
>>>>>> *james at supmenow.com <james at supmenow.com>⎥supmenow.com
>>>>>> <http://supmenow.com>*
>>>>>>
>>>>>> *Sup*
>>>>>>
>>>>>> *Runway East *
>>>>>>
>>>>>> *10 Finsbury Square*
>>>>>>
>>>>>> *London*
>>>>>>
>>>>>> * EC2A 1AF *
>>>>>>
>>>>>> On 16 August 2016 at 17:50, Haravikk <swift-evolution at haravikk.me>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>> On 16 Aug 2016, at 15:49, Xiaodi Wu via swift-evolution <
>>>>>>> swift-evolution at swift.org> wrote:
>>>>>>>
>>>>>>> I can see the use case, but it'd be annoying (or, impossible) to
>>>>>>> work around if I intend to call `end` by passing it to a helper function in
>>>>>>> another (let's say, precompiled) module. There's no way for the compiler to
>>>>>>> inspect that `end` is always called by that other module, and if calling
>>>>>>> `end` twice causes bad things to happen, I'm totally out of luck. You'd
>>>>>>> need a companion annotation to pass along the requirement to the callee, or
>>>>>>> some sort of force-unrequire, but the latter can't have teeth (i.e. can't
>>>>>>> enforce at runtime) if the closure is escaping.
>>>>>>> On Tue, Aug 16, 2016 at 08:39 James Campbell via swift-evolution <
>>>>>>> swift-evolution at swift.org> wrote:
>>>>>>>
>>>>>>>> It would be handy if a callback could be marked as required with an
>>>>>>>> optional descriptive message i.e
>>>>>>>>
>>>>>>>> class BackgroundTask {
>>>>>>>>  func run(end: @required("You must call end otherwise iOS will
>>>>>>>> penalise your app for being a bad citizen") () -> Void)
>>>>>>>> }
>>>>>>>>
>>>>>>>> That was the developer can comunicate the bad things that can
>>>>>>>> happen if this callback isn't called such as iOS peanlizing them for not
>>>>>>>> ending a background task or perhaps memory leaks caused by clean up code
>>>>>>>> unable to be triggered.
>>>>>>>>
>>>>>>>
>>>>>>> Could this not just behave in the same way as @noescape, in which
>>>>>>> case you can pass the closure on to other functions so long as they also
>>>>>>> have the @noescape attribute? In this case passing it as a parameter to
>>>>>>> another method with the @required attribute would be equivalent to calling
>>>>>>> it directly (since you know the other method must eventually call it).
>>>>>>>
>>>>>>
>>>>>>
>>>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160816/fa8bf61d/attachment.html>