NSObject的值(forKey :)无法在Swift 4中运行

Question

在Xcode 9 Beta中试用Swift 4.

出于某种原因,我在NSObject上使用键值访问器时遇到了崩溃.

有任何想法吗？

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).

Answer 1

键值编码需要Objective-C.在Swift 4中,您必须明确标记可从Obj-C访问的成员:

@objcMembers
class Person: NSObject {

要么

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

参见Swift Evolution 160

Answer 2

ObjC推理在Swift 4中受到限制.您可以使用objcMembers编译器标记您的类以生成符合ObjC的访问器:

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

或者通过在Build Settings 中将Swift 3 Objc Inference设置为On来恢复旧行为: