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

James Froggatt conductator at ntlworld.com
Mon Apr 25 14:18:02 CDT 2016

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.

------------ Begin Message ------------ 
Group: gmane.comp.lang.swift.evolution 
MsgID: <A57B248C-9679-450A-A09D-8C0A5E3846E8 at apple.com> 

Hello Swift community,

The review of "SE-0070: Make Optional Requirements Objective-C only" begins now and runs through May 2. The proposal is available here:


Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at


or, if you would like to keep your feedback private, directly to the review manager.

What goes into a review?

The goal of the review process is to improve the proposal under review through constructive criticism and, eventually, determine the direction of Swift. When writing your review, here are some questions you might want to answer in your review:

* What is your evaluation of the proposal?
* Is the problem being addressed significant enough to warrant a change to Swift?
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More information about the Swift evolution process is available at


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-Chris Lattner
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From James F

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