[swift-evolution] Guaranteed closure execution

[Andrew Bennett]

Hi, not beyond this thread that I have seen. I think it's worth you
summarizing this thread in a formal proposal and putting it up for
discussion or submitting it as a PR :)

On Sunday, 10 April 2016, Gwendal Roué <swift-evolution at swift.org> wrote:

> Hello all,
>
> I was wondering if this topic had evolved in anyway since its original
> introduction.
>
> @noescape(once) would still be a useful addition to the language!
>
> Gwendal Roué
>
>
>
> Le 3 févr. 2016 à 22:21, Félix Cloutier via swift-evolution <
> swift-evolution at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-evolution at swift.org');>> a écrit :
>
> I updated the proposal to address some concerns. It can be found at:
> https://github.com/zneak/swift-evolution/blob/master/proposals/00xx-noescape-once.md
>
> Things that changed:
>
>
>    - It now says that the closure must be called on code paths where the
>    function throws;
>    - you can have multiple @noescape(once) parameters but they can't make
>    assumptions from one another.
>
>
> I'm not 100% convinced that forcing a call on code paths that throw is
> always desirable. I've changed it because Chris's support probably means
> that the feature has better chances of making it, but I'm not convinced
> yet. If throwing allows me to return without calling the closure, I can
> write this:
>
> do {
> let foo: Int
> try withLock(someLock, timeout: 0.5) {
> foo = sharedThing.foo
> }
> } catch {
> print("couldn't acquire lock fast enough")
> }
>
> which would be kind of messy if instead, the closure needed a parameter to
> tell whether the lock was acquired or not when it runs.
>
> Félix
>
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>
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