> On 16 Aug 2016, at 15:49, Xiaodi Wu via swift-evolution
> <swift-evolution@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@swift.org <mailto:swift-evolution@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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