12-可选链

//可选链 1
class Car { var price = 0 }
class Dog { var weight = 0 }
class Person5 {
    var name: String = ""
    var dog: Dog = Dog()
    var car: Car? = Car()
    func age() -> Int { 18 }
    func eat() { print("Person eat") }
    subscript(index: Int) -> Int { index }
}
/*
 如果可选项为nil,调用方法、下标、属性失败，结果为nil,如果可选项不为nil,调用方法、下标、属性成功，结果会被包装成可选项。如果结果本来就是可选项，不会进行再次包装
 */
var person: Person5? = Person5()
var age1 = person!.age() //Int
var age2 = person?.age() //Int?
var name = person?.name //String?
var index = person?[6] //Int?
func getName() -> String {"jack"}
person?.name = getName() //如果person是nil不会调用getName()


if let _ = person?.eat() { //Person eat
    print("eat调用成功") //eat调用成功
} else {
    print("eat调用失败")
}
var dog = person?.dog //dog? //Optional(__lldb_expr_95.Dog)
var weight = person?.dog.weight //Int? //Optional(0)
var price = person?.car?.price //Int? //Optional(0)  //多个？可以链接在一起，如果链中任何一个节点是nil，那么整个链就会调用失败

var scores = ["Jack": [86, 82, 84], "Rose": [79, 94, 81]]
scores["Jack"]?[0] = 100
scores["Rose"]?[2] += 10
scores["Kate"]?[0] = 88
print(scores)  //["Rose": [79, 94, 91], "Jack": [100, 82, 84]]
var num1: Int? = 5
num1? = 10 //Optional(10)
var num2: Int? = nil
num2? = 10 //nil 因为num2已经为nil了
var dict: [String : (Int, Int) -> Int] = ["sum" : (+), "difference" : (-)]
var result = dict["sum"]?(10, 20) //Optional(30) Int?