swift 隐式可选型实例详解
1、隐式可选型的基本使用
varerrorMessage:String?=nil errorMessage="NotFound" "Themessageis"+errorMessage!
隐式可选型的定义
varerrorMessage:String!=nil errorMessage="NotFound" "Themessageis"+errorMessage
隐式可选型不需要解包，所以隐式可选型容易出错
以上程序当errorMessage为nil时程序会报错
2、隐式可选型的实际应用
//主要应用在类的成员变量的初始化上
classCity{
letcityName:String
unownedvarcountry:Country
init(cityName:String,country:Country){
self.cityName=cityName
self.country=country
}
}
classCountry{
letcountryName:String
varcapitalCity:City!
init(countryName:String,capitalCity:String){
self.countryName=countryName
self.capitalCity=City(cityName:capitalCity,country:self)
}
funcshowInfo(){
print("Thisis\(countryName).")
print("Thecapitalis\(capitalCity.cityName).")
}
}
letchina=Country(countryName:"China",capitalCity:"Beijing")
china.showInfo()
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