[swift-evolution] [swift-evolution-announce] [Review] SE-0153: Compensate for the inconsistency of @NSCopying's behaviour

[Torin Kwok]

I have already submitted a new pull-request <https://github.com/apple/swift-evolution/pull/617> for this modification to the proposal SE-0153. Please you guys feel free to submit your review on GitHub's File Changed page <https://github.com/apple/swift-evolution/pull/617/files> or just reply this mail directly. Thank you.

> On 18 Feb 2017, at 19:57, Torin Kwok <torin at kwok.im> wrote:
> 
> Proposal link:
> 
> https://github.com/apple/swift-evolution/blob/master/proposals/0153-compensate-for-the-inconsistency-of-nscopyings-behaviour.md <https://github.com/apple/swift-evolution/blob/master/proposals/0153-compensate-for-the-inconsistency-of-nscopyings-behaviour.md>
> Reply text:
> 
> However, occasionally a constructor might be non-copying on purpose, so we'll need a way to disable the warning.
> How about the determination method mentioned in the proposal:
> 
> ... if developers are performing an assignment operation from within an initializer between a property declared as @NSCopyingand an instance of a protocol conforming class.
> That is, there are two key factors determining whether a fixable error or warning should be emitted:
> 
> If the destination property has been declared as @NSCopying in class definition
> If the source value conforms to <NSCopying> protocol
> Once both are true, then what compiler can be sure about is that developer definitely missed the required manual copy invocation and it would emit either an error or a warning correspondingly. Otherwise, compiler would not complain of anything and would just leave the decision up to developers.
> 
> 
>> On 18 Feb 2017, at 18:16, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>>> On Feb 17, 2017, at 3:18 PM, Douglas Gregor <dgregor at apple.com <mailto:dgregor at apple.com>> wrote:
>>> 
>>> https://github.com/apple/swift-evolution/blob/master/proposals/0153-compensate-for-the-inconsistency-of-nscopyings-behaviour.md <https://github.com/apple/swift-evolution/blob/master/proposals/0153-compensate-for-the-inconsistency-of-nscopyings-behaviour.md>
>>> 
>>> 	• What is your evaluation of the proposal?
>> 
>> I think a warning is very appropriate.
>> 
>> However, occasionally a constructor might be non-copying on purpose, so we'll need a way to disable the warning. A few possibilities:
>> 
>> * Use .self on the value
>> * Parenthesize the value
>> * Parenthesize the variable
>> 
>> I don't favor using compiler magic. Too spooky.
>> 
>>> 	• Is the problem being addressed significant enough to warrant a change to Swift?
>> 
>> Yeah, that's a pretty easy mistake to make.
>> 
>>> 	• Does this proposal fit well with the feel and direction of Swift?
>> 
>> Yes. Swift usually tries to help you avoid mistakes.
>> 
>>> 	• If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
>> 
>> N/A.
>> 
>>> 	• How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
>> 
>> Quick reading.
>> 
>> -- 
>> Brent Royal-Gordon
>> Architechies
>> 
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>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-evolution
> 

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