[swift-evolution] Required Callback

[Xiaodi Wu]

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.
>
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> 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).
>>
>
>
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