swift 隐式 swift 隐式可选型实例详解

时间:2021-03-24 追到梦的魔术师人气:0

想了解swift 隐式可选型实例详解的相关内容吗，追到梦的魔术师在本文为您仔细讲解 swift 隐式的相关知识和一些Code实例，欢迎阅读和指正，我们先划重点：swift,隐式可选型,swift,隐式可选型分析，下面大家一起来学习吧。

1、隐式可选型的基本使用

var errorMessage: String? = nil
errorMessage = "Not Found"
"The message is " + errorMessage!

隐式可选型的定义

var errorMessage: String! = nil
errorMessage = "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

// 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()

感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！

加载全部内容