Swift 可选项 Optional

//可选项
var name:String?="jack"
print(name) //Optional("jack") //并且还有警告
var age:String?
age=nil
print(age)// nil
//如果直接不定义为可选类型、不能给改属性赋值为nil
// var a:String
//a=nil  //错误信息 ‘nil‘ cannot be assigned to type ‘String‘

var age:Int?=10
//如果要从可选项中取出被包装的数据(将盒子里装的东西取出来)，需要使用感叹号! 进行强制解包
var sage = age!

sage=sage+10
print(sage) //20

var a: Int? //默认为nil
//a! 如果对值为nil的可选项(空盒子)进行强制解包，将会产生运行时错误

var age:Int?=Int("aa") //"22" //转换成功22
if let p = age {
    print("转换成功\(p)")
}else{
    print("转换失败")
} //aa 转换失败

enum Season : Int {
    case spring = 1, summer, autumn, winter
}
//6 失败  1234 成功
if let season = Season(rawValue: 6) {
    switch season { case .spring:
        print("the season is spring")
    default:
        print("the season is other")
    }
} else {
    print("no such season")
}
//可选绑定并列条件句可以用，隔开
if let w = Int("33"),
let m = Int("44") {
      print("wm转换成功 w\(w)m\(m)")
}else{
    print("wm转换失败")
}//wm转换成功 w33m44
//while 循环中使用可选项绑定
//遍历数组，将遇到的正数都加起来，如果遇到负数或者非数字，停止遍历
var strs = ["10", "20", "abc", "-20", "30"]

var index = 0
var sum = 0


while let p = Int(strs[index]),p>0{
    sum+=p
    index+=1
}
print(sum) //30

let a: Int? = 1
let b: Int? = 2
let c = a ?? b // c是Int? , Optional(1)

let a: Int? = 1
let b: Int = 2
let c = a ?? b // c是Int , 1

let a: Int? = nil
let b: Int = 2
let c = a ?? b // c是Int , 2

let a: Int? = nil
let b: Int? = 2
let c = a ?? b // c是Int? , Optional(2)

let a: Int? = nil
let b: Int = 2
// 如果不使用??运算符 let c: Int
if let tmp = a {
    c = tmp
} else {
    c=b
}
let a: Int? = nil
let b: Int? = nil
let c = a ?? b // c是Int? , nil

//??跟if let配合使用
let a: Int? = nil
let b: Int? = 2
if let c = a ?? b {
    print(c)
}
// 类似于if a != nil || b != nil
if let c = a, let d = b {
    print(c)
    print(d)
}
// 类似于if a != nil && b != nil

func test(){
    guard let p = Int("33") else {
        return
    }
    guard let q = Int("44") else {
        return
    }
    print(p,q)
}

test() // 33 、4

let num1: Int! = 10
let num2: Int = num1
if num1 != nil {
    print(num1 + 6) // 16
}
if let num3 = num1 {
    print(num3)
}
let num1: Int! = nil
// Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value
let num2: Int = num1