1、隐式可选型的基本使用
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var errorMessage: String? = nilerrorMessage = "Not Found""The message is " + errorMessage! |
隐式可选型的定义
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var errorMessage: String! = nilerrorMessage = "Not Found""The message is " + 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
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// 主要应用在类的成员变量的初始化上class City{ let cityName: String unowned var country: Country init( cityName: String , country: Country){ self.cityName = cityName self.country = country }}class Country{ let countryName: String var capitalCity: City! init( countryName: String , capitalCity: String ){ self.countryName = countryName self.capitalCity = City(cityName: capitalCity, country: self) } func showInfo(){ print("This is \(countryName).") print("The capital is \(capitalCity.cityName).") }}let china = Country(countryName: "China", capitalCity: "Beijing")china.showInfo() |
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原文链接：http://blog.csdn.net/u012903898/article/details/52929881
