[swift-evolution] [Review] SE-0140: Bridge Optional As Its Payload Or NSNull

David Hart david at hartbit.com
Wed Sep 7 02:52:48 CDT 2016

I’’ve been migrating a project to Swift 3 and a the piece of code below did not require any modification but had wildly different results:

let myView = viewController.view
        item: myView, attribute: .left,
        relatedBy: .equal,
        toItem: superview, attribute: .left,
        multiplier: 1, constant: 0)

UIViewController’s view property is typed as UIView! so myView’s type is inferred to UIView? in Swift 3 (previous inferred as UIView! in Swift 2). This will crash in Swift 3 (not in Swift 2), because I think that myView’s optional value is not bridged to the wrapped value in Objective-C when passed to NSLayoutConstraint. Can somebody confirm that this proposal fixes this issue?


> On 03 Sep 2016, at 00:50, Douglas Gregor via swift-evolution <swift-evolution at swift.org> wrote:
> Hello Swift community,
> The review of SE-0140 "Bridge Optional As Its Payload Or NSNull" begins now and runs through September 8, 2016. The proposal is available here:
> https://github.com/apple/swift-evolution/blob/master/proposals/0140-bridge-optional-to-nsnull.md <https://github.com/apple/swift-evolution/blob/master/proposals/0140-bridge-optional-to-nsnull.md>
> Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at
> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
> or, if you would like to keep your feedback private, directly to the review manager. When replying, please try to keep the proposal link at the top of the message:
> Proposal link:
> https://github.com/apple/swift-evolution/blob/master/proposals/0140-bridge-optional-to-nsnull.md <https://github.com/apple/swift-evolution/blob/master/proposals/0140-bridge-optional-to-nsnull.md>
> Reply text
> Other replies
>  <https://github.com/apple/swift-evolution#what-goes-into-a-review-1>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?
> Does this proposal fit well with the feel and direction of Swift?
> If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
> How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
> More information about the Swift evolution process is available at
> https://github.com/apple/swift-evolution/blob/master/process.md <https://github.com/apple/swift-evolution/blob/master/process.md>
> Thank you,
> -Doug
> Review Manager
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