[swift-evolution] [swift-evolution-announce] [Review] SE-0083: Remove bridging conversion behavior from dynamic casts

[Jed Lewison]

The proposal also suggests:

extension _ObjectiveCBridgeable {
    init?(bridging object: AnyObject)
}

Which would yield:

let foo: AnyObject = NSString(string: "String")
let bar = String(bridging: foo) // “String"

let foo2: AnyObject = NSArray(array: [])
let bar2 = String(bridging: foo) // nil

The code in the proposal works OOB in Swift 2.2 for String/Double/Float, but not Array and Dictionary. Not sure if it already would work in Swift 3.0 for that, or there would need to be a little more work done.

> On May 23, 2016, at 8:22 PM, Jordan Rose <jordan_rose at apple.com> wrote:
> 
> Let’s see…
> 
> let name = plist[“name”].bridge() as String
> 
> Not the worst, but definitely better than any of the alternatives below. Unfortunately, I think that “if” is out of the question, at least for Swift 3.
> 
> Jordan
> 
>> On May 23, 2016, at 20:21, Jed Lewison <jed.lewison at icloud.com <mailto:jed.lewison at icloud.com>> wrote:
>> 
>> If we could have extensions on AnyObject, a simple .bridge() would do the trick, right? (Assuming bridge was generic.) I think something along those lines was mentioned in the proposal.
>> 
>> Sent from my iPhone
>> 
>> On May 23, 2016, at 5:26 PM, Jordan Rose via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>>> I am way late, but I share Brent’s concerns. I don’t think this addresses the very common case of “getting a String out of a heterogeneous dictionary”.
>>> 
>>> let name = plist[“name”] as! String
>>> 
>>> becomes one of these:
>>> 
>>> let name = plist[“name”] as! NSString as String
>>> let name = String(plist[“name”] as! NSString)
>>> let name = String(forceBridging: plist[“name”]) // not in the proposal
>>> 
>>> none of which I’m particularly happy with. 
>>> 
>>> Jordan
>>> 
>>> 
>>>> On May 19, 2016, at 02:31, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>> 
>>>>> 	* What is your evaluation of the proposal?
>>>> 
>>>> The review is technically over, but I don't believe a decision has been announced yet, so...
>>>> 
>>>> I am generally in favor, but I have a serious concern about the readability of certain conversions with this change. To wit, conversions like these:
>>>> 
>>>> 	myArray as! [NSView]
>>>> 	myDictionary as! [String: NSView]
>>>> 
>>>> Are about to become something more like these:
>>>> 
>>>> 	[NSView](forcedLazyBridging: myArray)
>>>> 	[String: NSView](forcedLazyBridging: myDictionary)
>>>> 	
>>>> Or these:
>>>> 
>>>> 	Array<NSView>(forcedLazyBridging: myArray)
>>>> 	Dictionary<String, NSView>(forcedLazyBridging: myDictionary)
>>>> 
>>>> Either option is a significant regression in code readability compared to the status quo.
>>>> 
>>>> It's enough to make me wonder if we shouldn't have special-cased conversion methods for NSArray, NSDictionary, and NSSet:
>>>> 
>>>> 	myArray.of(NSView)				// returns [NSView]
>>>> 	myDictionary.of(NSView, for: String) 	// returns [String: NSView]
>>>> 	mySet.of(NSView)					// returns Set<NSView>
>>>> 
>>>> On the other hand, if you *don't* have to specify an element type, these aren't so bad:
>>>> 
>>>> 	Array(forcedLazyBridging: myArray)
>>>> 	Dictionary(forcedLazyBridging: myDictionary)
>>>> 
>>>> And it gets even better if you use something a little saner than `forcedLazyBridging` for the label.
>>>> 
>>>>> 	* Is the problem being addressed significant enough to warrant a change to Swift?
>>>> 
>>>> Yes. Conversions are a mess, and it'll be nice to clean them up.
>>>> 
>>>>> 	* Does this proposal fit well with the feel and direction of Swift?
>>>> 
>>>> Yes.
>>>> 
>>>>> 	* If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
>>>> 
>>>> Most languages I've used have had much simpler cast systems with nothing particularly close to Swift's bridging casts.
>>>> 
>>>>> 	* How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
>>>> 
>>>> Quick reading.
>>>> 
>>>> -- 
>>>> Brent Royal-Gordon
>>>> Architechies
>>>> 
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>>> 
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> 

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