옵셔널 체이닝과 오류 처리 기초

소개

옵셔널 체이닝

struct User { var address: Address? }
struct Address { var city: String }
let u: User? = User(address: Address(city: "Paris"))
print(u?.address?.city)   // Optional("Paris")

guard 패턴

func greet(_ name: String?) {
    guard let n = name else {
        print("No name")
        return
    }
    print("Hello, \\(n)!")
}
greet(nil)
greet("Ada")

try?와 try!

enum ParseErr: Error { case bad }
func parse(_ s: String) throws -> Int {
    guard let n = Int(s) else { throw ParseErr.bad }
    return n
}
let ok = try? parse("10")   // Int?
let fail = try? parse("xx") // nil
// let crash = try! parse("xx")  // runtime crash

do/catch

do {
    let n = try parse("42")
    print(n)
} catch {
    print("error:", error)
}

Result 타입

func safeParse(_ s: String) -> Result<Int,Error> {
    do { return .success(try parse(s)) }
    catch { return .failure(error) }
}
print(safeParse("5"))
print(safeParse("oops"))

옵셔널 체이닝 질문

복습