Value (forKey :) for NSObject doesn't work in Swift 4

Question

Value (forKey :) for NSObject doesn't work in Swift 4

Trying Swift 4 in Xcode 9 beta.

For some reason I am getting a crash when using keyword access on NSObject.

Any ideas?

import Cocoa

class Person: NSObject {
    var name = ""
    var age = 0
}

let alpha = Person()
alpha.name = "Robert"
alpha.age = 53

alpha.value(forKey: "name")
// error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0).

+3

swift swift4

closetCoder 09 June 17 at 15:29

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2 answers

Sulthan · Answer 1 · 2017-06-09T15:34:38+0000

Objective-C is required to encode the key value. In Swift 4, you have to explicitly mark the members available from Obj-C:

@objcMembers
class Person: NSObject {

or

class Person: NSObject {
    @objc var name = ""
    var age = 0
}

See Swift Evolution 160

Code Different · Answer 2 · 2017-06-09T15:37:03+0000

ObjC inference was limited in Swift 4. You can mark your class objcMembers

so the compiler can generate ObjC compatible accessors

@objcMembers
class Person: NSObject {
    var name = ""
    var age = 0
}

Or revert the previous behavior by setting Swift 3 Objc Inference to On on Build Settings:

Value (forKey :) for NSObject doesn't work in Swift 4

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