옵셔널 입문: ?, nil, if let, guard let, ??

옵셔널이란 무엇인가요?

if let 바인딩

var nickname: String? = nil
print("nickname =", String(describing: nickname))

// Optional binding with if let
let input: String? = "Ada"
if let name = input {
    print("Hello, \\(name)")
} else {
    print("No name")
}

guard let

func greet(_ maybeName: String?) {
    guard let name = maybeName else {
        print("Missing name"); return
    }
    print("Hi, \\(name)!")
}
greet(nil)
greet("Grace")

nil 병합(??)

let provided: String? = nil
let username = provided ?? "Guest"
print("Username:", username)

옵셔널 체이닝

struct Profile { var city: String? }
struct User { var profile: Profile? }

let u1 = User(profile: Profile(city: "Paris"))
let u2 = User(profile: nil)

// Optional chaining safely traverses missing links
print(u1.profile?.city?.uppercased() ?? "No city")  // "PARIS"
print(u2.profile?.city ?? "No city")                // "No city"

팁과 주의할 점

guard let의 동작

복습