> Le 23 avr. 2016 à 18:33, Timothy Wood <[email protected]> a écrit :
>
>
>
>> On Apr 23, 2016, at 5:56 AM, Gwendal Roué via swift-evolution
>> <[email protected]>
> [...]
>>
>> Since @once actually implies @noescape (as described earlier in the thread),
>> it can be shortened to:
> [...]
>
> I'm surprised that @once would imply @noescape. In my opinion this makes it
> much less useful. For example, it is common to have asynchronous operations
> with a completion handler -- the completion handler will definitely escape
> and should definitely get called once.
I'm sorry but the goal of this proposal is not abstract, but very very very
concrete:
let x: Int
f { x = 1 }
// use x without compiler error
If you break this (and you do), you miss the point entirely.
> In some cases the completion handler may get passed to other functions that
> take an @once block, so that should count as passing off your responsibility
> to call it.
>
> In other cases, it may get stored in an object representing a long-lived
> async operation. This is trickier, but I would hope that a nullable var
> property, only in a reference type, could be marked @once. Reading that
> property would return an @once block *and* clear the property (so you'd be
> back to needing to call it or pass it away). It is unclear if only closure
> properties should be allowed to be marked @once, but presumable the
> implementation cloud support any type.
>
> A simple noescape @once might find a few trivial uses in my codebase, but the
> really hard to diagnose bugs have been in async code where escaping is
> natural and necessary.
You are describing another proposal. Please please please please don't pollute
this one.
Gwendal Roué
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