Swift 计算属性上的 KVO

的文章如下：

swift
class Person: NSObject {
    @objc dynamic var name: String = ""
    
    var fullName: String {
        return "My name is " + name
    }
}
class Observer: NSObject {
    @objc func nameDidChange(_ change: [NSKeyValueChangeKey : Any]?) {
        print("Name did change")
    }
}
let person = Person()
let observer = Observer()
person.addObserver(observer, forKeyPath: #keyPath(Person.fullName), options: .new, context: nil)
person.name = "John" // 触发KVO通知
person.removeObserver(observer, forKeyPath: #keyPath(Person.fullName))