importFoundation
//***********************************************************************************************
//1.Optional Chaining(自判断链接）
//_______________________________________________________________________________________________
//介绍
//自判断链接是一种可以请求和调用属性，方法以及子脚本的过程，他的自判断性体现于请求或者调用的目标当前可能为空。如果自判断的目标有值，那么他的调用就会成功；如果目标为空，返回 nil
//***********************************************************************************************
//2.Optional Chaining as an Alternative to Forced Unwrapping（自判断链接可以替代强制拆包）
//通过在想调用属性，方法，或者子脚本的自判断值（非空）后放一个问号，可以定义一个自判断链接。
//_______________________________________________________________________________________________
class Person{ //Person 具有一个自判断 residence 属性
var residence: Residence?
}
class Residence{ //Residence 具有一个 Int 类型的 numberOfRooms
var numberOfRooms = 1
}
let john = Person() //因为 Person 类中 residence 为自判断型，所以在创建实例的时候 residence 属性默认为空
//let roomCount = john.residence!.numberOfRooms //如果我们此刻想要强制拆包的话，因为 john.residence 为 nil，程序错误，只有当 john.residence 不为空的时候，程序才能运行
if let roomCount = john.residence?.numberOfRooms{ //使用自判断链接提供了另外一种方式去获取类实例属性，这时不会抱错，而是以 nil 的形式表示 john.residence
println("john's residence has \(roomCount) room")
}
else{
println("Unable to retrieve the number of rooms")
}
john.residence = Residence() //自己定义一个 Residence 实例给 john.residence ， 这时它就不是空了
if let roomCount = john.residence?.numberOfRooms{
//3.Defining Model Classes for Optional Chaining（为自判断链接定义模型类）
class Person1{
var residence1: Residence1?
}
class Residence1{
var rooms = [Room]() //初始化 rooms 为一个空数组，存储的元素必须为 Room 类型
var numberOfRooms: Int{
return rooms.count
}
subscript(i: Int) -> Room{ //为了快速访问 rooms 数组， Residence1 定义了一个只读的子脚本，通过插入角标就可以成功调用
return rooms[i]
}
func printNumberOfRooms(){ //打印房间个数
println("The number of rooms is \(numberOfRooms)")
}
var address: Address?
}
class Room{
let name: String
init(name: String){
self.name = name
}
}
class Address{
var buildingName: String?
var buildingNumber: String?
var street: String?
func buildingIdentifier() -> String?{
if (buildingName != nil){
return buildingName
}
else{
return nil
}
}
}
//4.Calling Properties Through Optional Chaining（通过自判断链接调用属性）
//代码演示使用自判断链接替代强制拆包获取属性，并且检查属性是否获取成功
let john1 = Person1()
if let roomCount = john1.residence1?.numberOfRooms{ //由于 john1.residence1 为 nil，所以执行 else 中的语句
println("john's residence has \(roomCount) rooms")
}
println("Unabel to retrieve the number of rooms")
}
//5.Calling Methods Through Optional Chaining（通过自判断链接调用方法）
if john1.residence1?.printNumberOfRooms() != nil {
println("is was possible to print the number of rooms")
}
println("it was not possible to print the number of rooms")
}
//6.Calling Subscripts Through Optional Chaining（通过自判断链接调用子脚本）
if let firstRoomName = john1.residence1?[0].name {
println("The first room is \(firstRoomName)")
}
println("Unable to retrieve the first room name")
}
let Listo = Residence1()
Listo.rooms.append(Room(name: "Pin"))
Listo.rooms.append(Room(name: "Melody"))
john1.residence1 = Listo //给 john1.residence1 创建实例
if let firstRoomName = john1.residence1?[0].name{
println("the first room is \(firstRoomName)")
}
println("Unable to retrieve the first room name")
}
//7.CLinking Multiple Levels of Chaining（连接多层链接）
if let johnsStreet = john1.residence1?.address?.street{ //此时 john1.residence1 不是 nil，但 john1.residence1.address为 nil，所以返回 else 语句
println("john's street name is \(johnsStreet)")
}
println("Unable to retrieve the address")
}
let address = Address()
address.buildingName = "The Larches"
address.street = "laurel Street"
john1.residence1!.address = address //为 john1.residence1.address 赋值
println("Unable to retrieve the address")
}
//8.Chaining on Methods With Optional Return Values（链接自判断返回值的方法）
if let buildingIdentifier = john1.residence1?.address?.buildingIdentifier(){
println("john's building identifier is \(buildingIdentifier)") //返回的值依旧是 String 类型的自判断链接
}
if let buildingIdentifier = john1.residence1?.address?.buildingIdentifier()?.uppercaseString{ //当继续对自判断链接执行操作室，使用 ?. 来间隔方法
println("john's building identifier is \(buildingIdentifier)") //类型的自判断链接
}
