iOS / Swift Error throw, throws, try, catch

summary

Error를 throw하고 throws catch 하는 방법 간단히 정리
Swift5, Xcode10

addnew function

func addNew(username: String, password: String) throws -> Bool {        
    // do something...

    guard status == errSecSuccess else {
        throw KeychainError.unhandledError(status: status)
    }
    return true
}

viewDidLoad

 override func viewDidLoad() {
    super.viewDidLoad()

    let ret = try? addNew(username: username, password: password)
    if ret == false {
        print("failed")
    } else {
        print("success!")
    }        
}
// or
override func viewDidLoad() {
    super.viewDidLoad()

    do {
        let _ = try addNew(username: username, password: password)
    } catch {
        print(error.localizedDescription)
    }
}

Error enum

enum KeychainError: Error {
    case noPassword
    case unexpectedPasswordData
    case unhandledError(status: OSStatus)
}