On Mon, May 8, 2017 at 7:57 AM, David Hart <da...@hartbit.com> wrote: > Sounds great! It should be an easy one to get through,
Thanks David, appreciate it :) I've created a draft of the proposal. Any feedback would be very welcome. I wasn't sure if there was an effect on ABI stability or API resilience. I don't think there would be as this is only correcting syntax. Also, just adding the link again where I had a try at implementing the warning/error. Hopefully that can be helpful in getting feedback about the proposal as well. https://github.com/gspiers/swift/commit/ecde3ec5f61f259f8a396618e9973bac04536fd0 # Remove ownership keyword support in protocols * Proposal: [SE-NNNN](NNNN-remove-ownership-keyword-support-in-protocols.md) * Authors: [Greg Spiers](https://github.com/gspiers) * Review Manager: TBD * Status: * Bug: [SR-479](https://bugs.swift.org/browse/SR-479) ## Introduction This proposal removes support for the keywords `weak` and `unowned` for property declarations in a protocol. Swift-evolution thread: [Ownership on protocol property requirements](https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170501/036495.html) thread. (TODO: Add link to rest of discussion) ## Motivation Currently it's possible to use the weak/unowned keywords for a property requirement in a protocol. This can lead to confusion as specifying one of these keywords does not enforce or raise any warnings in the adopting type of that protocol: ```swift class A {} protocol P { weak var weakVar: A? { get set } } class B: P { var weakVar: A? // Not declared weak, no compiler warning/error } ``` This can lead to unexpected and surprising behaviour from the point of view of users. They keywords themselves are currently meaningless inside of a protocol but look like they would have an effect when the protocol is adopted. ## Proposed solution Although the case could be made that the keywords should have meaning in a protocol, as they are currently implemented today they don't have an effect. This proposal aims to cleanup the misleading syntax and isn't meant to remove functionality only correct to existing behaviour. This proposal suggests removing support for `weak` and `unowned` in a protocol. ## Detailed design The compiler will flag the use of `weak` and `unowned` in a protocol and suggest a fix to remove the keyword. ## Source compatibility This is a source breaking change but one that would only correct code that is already has broken assumptions. For existing use the compiler will raise a compilation error. When running in Swift 3 mode a warning can be generated instead of an error. It could be possible to address source compatibility through source migration as well. ## Effect on ABI stability This proposal does not affect ABI stability. ## Effect on API resilience This proposal should not effect API resilience. ## Alternatives considered There is an argument in making `weak` and `unowned` have meaning in a protocol but this does open up other questions and is probably better as a topic of a separate discussion/proposal. As this would be additive it can be addressed at a later point when we have a clearer understanding. _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
