小编pro*_*oxi的帖子

我正在努力在Swift 4中使用新的强类型KVO语法来观察仅通过协议可见的属性:

import Cocoa

@objc protocol Observable: class {
    var bar: Int { get }
}

@objc class Foo: NSObject, Observable {
    @objc dynamic var bar = 42
}

let implementation = Foo()

let observable: Observable = implementation

let observation = observable.observe(\.bar, options: .new) { _, change in
    guard let newValue = change.newValue else { return }

    print(newValue)
}

implementation.bar = 50

error: value of type 'Observable' has no member 'observe'
let observation = observable.observe(\.bar, options: .new) { _, change …