'self' 在所有存储的属性被初始化之前使用 [英] 'self' used before all stored properties are initialized

问题描述

我正在处理 learn-swift playground 并在我学习该语言时将其升级到 Swift 2.0.以下代码(可能适用于早期版本的 Swift)现在会生成两个错误:在所有存储属性初始化之前使用'self'"和在初始化之前使用常量'self.capitalCity'"

I'm working through a learn-swift playground and upgrading it to Swift 2.0 as I learn the language. The following code (which likely worked with prior versions of Swift) now generates two errors: "'self' used before all stored properties are initialized" and "Constant 'self.capitalCity' used before initialized"

class Country
{
    let name: String
    let capitalCity: City!

    init(name: String, capitalName: String)
    {
        self.name = name
        self.capitalCity = City(name: capitalName, country: self)
    }
}

class City
{
    let name: String
    unowned let country: Country

    init(name: String, country: Country)
    {
        self.name = name
        self.country = country
    }
}

阅读回答类似的问题 我看到我可以将 let capitalCity: City! 更改为 var capitalCity: City! 并解决语法错误.

reading an answer to a similar question I see that I can change let capitalCity: City! to var capitalCity: City! and the syntax error is resolved.

我意识到在这个人为的例子中，一个国家的首都可以改变，所以这很好，但是如果有一个值真的是一个常数的情况......

I realize that in this contrived example a country's capital city can change, so that would be fine, but what if there were a case where the value really was a constant...

有什么方法可以解决语法错误，同时保持 capitalCity 不变?

Is there any way to resolve the syntax error while keeping capitalCity a constant?

推荐答案

在这种情况下，我建议您将属性设置为变量，但通过计算属性将其隐藏(使其看起来像常量):

In this case I would suggest you to make the property a variable but hiding it (make it seem like a constant) through a computed property:

class Country {
    let name: String

    private var _capitalCity: City!
    var capitalCity: City {
        return _capitalCity
    }

    init(name: String, capitalName: String) {
        self.name = name
        self._capitalCity = City(name: capitalName, country: self)
    }
}

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