属性 – Swift类中的错误：属性未在super.init调用初始化

概述我有两个类，Shape和Square class Shape { var numberOfSides = 0 var name: String init(name:String) { self.name = name } func simpleDescription() -> String { return "A shape 我有两个类，Shape和Square

class Shape {    var numberOfSIDes = 0    var name: String    init(name:String) {        self.name = name    }    func simpleDescription() -> String {        return "A shape with \(numberOfSIDes) sIDes."    }}class Square: Shape {    var sIDeLength: Double    init(sIDeLength:Double,name:String) {        super.init(name:name) // Error here        self.sIDeLength = sIDeLength        numberOfSIDes = 4    }    func area () -> Double {        return sIDeLength * sIDeLength    }}

使用上面的实现我得到错误：

property 'self.sIDeLength' not initialized at super.init call    super.init(name:name)

为什么我必须在调用super.init之前设置self.sIDeLength？

报价从Swift编程语言，它回答你的问题：

“Swift’s compiler performs four helpful safety-checks to make sure
that two-phase initialization is completed without error:”

Safety check 1 “A designated initializer must ensure that all of the
“propertIEs introduced by its class are initialized before it
delegates up to a superclass initializer.”

Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. 07000

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