[swift-evolution] [Review] SE-0070: Make Optional Requirements Objective-C only

[Douglas Gregor]

> On Apr 25, 2016, at 12:18 PM, James Froggatt via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Eliminating optional protocol requirements is fine by me. The proposal mentions ‘correcting’ the optional protocol requirement pattern by changing the methods to optional closure properties, but my feeling is that this ‘solution’ just acts to continue and perhaps encourage the anti-pattern established by ObjC. I think a native Swift design would be much better off using optional closure properties on the table view itself.
> 
> A common theme in these ObjC optional protocol requirements is the first parameter being an instance whichever class ‘requires’ the method. Yet on the rare occasion of the instance potentially having more than one value, the implementation for each instance is often so different that my first action will be to add a switch between the possible instances (which, of course, means having those components available as IBOutlet properties anyway).
> 
> I suggest a much better solution to optional protocol requirements in Swift is the creation of wrappers for UIKit components. These would implement the protocol requirements, and expose optional closure properties for their their public API. Making them properties makes it far clearer that the behaviour of the container will change if a value is provided, and would remove the persistent need to apply @objc to any Swift types dealing with UIKit. I understand this would be a manual task, but I just don't think there is a good automatic solution to this problem.

There are ~800 optional requirements in the iOS SDK and ~1000 in the OS X SDK. That too large a manual task to accomplish.

Also, I think the arguments in the proposal against the optional-closure-properties approach are fairly strong: it doesn’t seem like a good way to model Objective-C optional requirements.

	- Doug


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> Hello Swift community,
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> The review of "SE-0070: Make Optional Requirements Objective-C only" begins now and runs through May 2. The proposal is available here:
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> https://github.com/apple/swift-evolution/blob/master/proposals/0070-optional-requirements.md
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