Swift中的Getter和Setter – 使用WillSet和DidSet是否有意义？

>是的,willCheck是您唯一的选择
>只读属性分为两种类型：(a)其值来自其他属性的那些,例如,它们的总和; (b)您希望能够自行更改但不能由用户更改的内容.第一种类型真的没有二传;第二种类型有一个公共吸气剂和一个私人二传手.编译器可以帮助您检查它,程序将无法编译.如果在didSet中抛出fatalError,则会出现运行时错误,应用程序将崩溃.
>可能存在您不希望用户自由处理的状态对象,是的,您可以完全隐藏用户的状态.

您的代码第一个示例在定义支持变量时过于冗长 – 您不需要这样做.为了说明这些要点：

class Test
{
    // 1. Validate the new value
    var mustBeginWithA: String = "A word" {
        willSet {
            if !newValue.hasPrefix("A") {
                fatalError("This property must begin with the letter A")
            }
        }
    }

    // 2. A readonly property
    var x: Int = 1
    var y: Int = 2
    var total: Int {
        get { return x + y }
    }

    private(set) var greeting: String = "Hello world"
    func changeGreeting() {
        self.greeting = "Goodbye world" // Even for private property,you may still
                                        // want to set it,just not allowing the user
                                        // to do so
    }

    // 3. Hide implementation detail
    private var person = ["firstName": "","lastName": ""]
    var firstName: String {
        get { return person["firstName"]! }
        set { person["firstName"] = newValue }
    }

    var lastName: String {
        get { return person["lastName"]! }
        set { person["lastName"] = newValue }
    }

    var fullName: String {
        get { return self.firstName + " " + self.lastName }
        set {
            let components = newValue.componentsSeparatedByString(" ")
            self.firstName = components[0]
            self.lastName = components[1]
        }
    }
}

用法：

let t = Test()
t.mustBeginWithA = "Bee"        // runtime error

t.total = 30                    // Won't compile

t.greeting = "Goodbye world"    // Won't compile. The compiler does the check for you
                                // instead of a crash at run time

t.changeGreeting()              // OK,greeting now changed to "Goodbye world"

t.firstName = "John"            // Users have no idea that they are actually changing 
t.lastName = "Smith"            // a key in the dictionary and there's no way for them
                                // to access that dictionary

t.fullName = "Bart Simpsons"    // You do not want the user to change the full name
                                // without making a corresponding change in the
                                // firstName and lastName. With a custome setter,you
                                // can update both firstName and lastName to maintain
                                // consistency

关于Swift 2与Swift 3中的私密性的说明：如果你在Swift 2游乐场试试这个,你会发现t.greeting =“Goodbye world”的效果很好.这是因为Swift 2有一个奇怪的访问级别说明符：private表示“只能在当前文件中访问”.将类定义和示例代码分成不同的文件,Xcode会抱怨.在Swift 3中,它被更改为fileprivate,它更清晰,并保存private关键字,以便更类似于Java和.NET