오류 처리 연산자

컴바인의 오류

실패 타입

let publisher: AnyPublisher<Data, URLError> = apiClient.request()
// Output = Data, Failure = URLError

오류 가로채기

apiClient.fetchUser()
    .catch { error in
        Just(User.guest)
    }
    .sink { user in
        print("Got", user.name)
    }
    .store(in: &cancellables)

replaceError

apiClient.fetchCount()
    .replaceError(with: 0)
    .sink { count in
        self.badge.text = "\(count)"
    }
    .store(in: &cancellables)

retry

apiClient.fetchData()
    .retry(3)
    .sink(receiveCompletion: { print($0) },
          receiveValue: { print($0) })
    .store(in: &cancellables)

retry와 catch 조합하기

apiClient.fetchData()
    .retry(2)
    .catch { _ in
        Just(Data())
    }
    .sink { data in
        self.process(data)
    }
    .store(in: &cancellables)

mapError

enum AppError: Error { case network }

apiClient.request()
    .mapError { _ in AppError.network }
    .sink(receiveCompletion: { _ in }, receiveValue: { _ in })
    .store(in: &cancellables)

mapError가 중요한 이유

setFailureType

Just(42)
    .setFailureType(to: AppError.self)
    .merge(with: failablePublisher)
    .sink(receiveCompletion: { _ in }, receiveValue: { _ in })
    .store(in: &cancellables)

완료 처리

publisher.sink(
    receiveCompletion: { completion in
        if case .failure(let error) = completion {
            self.showAlert(error)
        }
    },
    receiveValue: { value in
        self.update(value)
    }
).store(in: &cancellables)

복원력 있는 파이프라인 설계

빠른 확인

요약