[swift-evolution] [Review] SE-0116: Import Objective-C id as Swift Any type

[Ben Langmuir]

Hey Joe,

I’m +1 on the overall direction, but I have some questions/concerns about the "Ambivalent dynamic casting from Any” section.

1) When you suggest that `x as String` succeeds but `x as NSString` fails, I assume this would only be true *after* SE-0083, since otherwise we’d be violating transitivity of `as` casts?

2) Have you considered the only allowing `as` casts to the bridged type (e.g. String) for values coming from `id` at the language level, but providing some guaranteed optimization that if you immediately convert to the ObjC class type (ie. NSString(x as! String)) we give zero-cost round-tripping? Would that be detectable?  I think making `value as? NSFoo` fail or succeed depending on whether the value came from ObjC  will be a source of subtle bugs.  What if I have multiple sources of values - some from ObjC, some from Swift - and stuff them into an [Any].

Ben

> On Jul 5, 2016, at 8:45 AM, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Hello Swift community,
> 
> The review of "SE-0116: Import Objective-C id as Swift Any type" begins now and runs through July 11. The proposal is available here:
> 
> 	https://github.com/apple/swift-evolution/blob/master/proposals/0116-id-as-any.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
> 
> 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 contribute to 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
> 
> Thank you,
> 
> -Chris Lattner
> Review Manager
> 
> 
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