swift 3 array of structs -> cast to NSObject -> cast back => crash

Question

The following code crashes on Swift 3, can anyone please explain why?

struct S {
    let a:Int
}

let t = [S(a: 8)]
let u:AnyObject = t as NSObject
let v:[S] = u as! [S]

Is that because in Swift 3 array of structs is NSObject (it's not in Swift 2) and it somehow can't be converted to NSArray well? And why is it NSObject?..

Does `let u:AnyObject = t as NSObject` even compile for you...? Arrays in swift are value types and does naturally not derive from the concrete class type `NSObject`. In Swift 2 implicit bridging between Swift native types and Obj-C types could allow for slightly confusing conversions, but implicit bridging facilities has been removed in Swift 3. — dfrib, Oct 19 '16 at 14:50
@silyevsk Ok, I've only tested for Swift 3 at the IBM sandbox (where it does not work). — dfrib, Oct 19 '16 at 15:24
@JAL - indeed, and then the optional can be unwrapped, so you solved the issue for me :) — silyevsk, Oct 19 '16 at 15:30

score 3 · Accepted Answer · answered Oct 19 '16 at 15:32

3

A possible solution would be to use a conditional binding with an optional downcast:

if let v = u as? [S] { /* */ }

Not sure why forced downcast wouldn't work though. Might be something funky going on with NSObject.

answered Oct 19 '16 at 15:32

JAL

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swift 3 array of structs -> cast to NSObject -> cast back => crash

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