问题描述
我正在通过学习swift游乐场,并在我学习该语言时将其升级到Swift 2.0.下面的代码(可能与Swift的早期版本一起使用)现在会产生两个错误:在初始化所有存储属性之前使用'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,我看到可以将let capitalCity: City!
更改为var capitalCity: City!
,并且语法错误已解决.
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,这样就可以了,但是如果在某些情况下其价值确实是不变的,那该怎么办...
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...
有什么办法可以在保持大写城市不变的情况下解决语法错误?
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(使其看起来像是常量):
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)
}
}
这篇关于在初始化所有存储的属性之前使用“自我"的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!