Swift类中的错误：属性未在super.init调用时初始化 [英] Error in Swift class: Property not initialized at super.init call

问题描述

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 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
    }
}

上面的实现我得到错误：

With the implementation above I get the error:

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

为什么我必须设置 self。在调用 super.init 之前

推荐答案

p> Swift编程语言的报价，它回答了你的问题：

Quote from The Swift Programming Language, which answers your question:

Swift的编译器执行四个有用的安全检查， $ b两阶段初始化完成没有错误：

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

安全检查1指定的初始化程序必须确保其引入的所有
属性类在初始化之前
委托给一个超类初始化器。

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."

摘录：Apple Inc.Swift编程语言iBooks。
https://itunes.apple.com/us/book/ swift-programming-language / id881256329？mt = 11

Excerpt From: Apple Inc. "The Swift Programming Language." iBooks. https://itunes.apple.com/us/book/swift-programming-language/id881256329?mt=11

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