try await와 오류 전파

시도 후 기다리기를 사용하는 이유

오류를 던지는 비동기 함수 + do/catch

enum NetError: Error { case offline; case badStatus(Int) }

func fetchNumber(from ok: Bool) async throws -> Int {
    try await Task.sleep(nanoseconds: 100_000_000)
    if !ok { throw NetError.offline }
    return 7
}

Task {
    do {
        let n = try await fetchNumber(from: true)
        print("value:", n)          // 7
    } catch {
        print("failed:", error)     // handled here
    }
}

오류 변환

Task {
    // try? converts failure to nil
    let maybe = try? await fetchNumber(from: false)
    print("optional result:", String(describing: maybe)) // nil on error

    // ⚠️ try! will crash if an error is thrown — avoid in production
    // let forced = try! await fetchNumber(from: false)
}

오류 올려 보내기

func loadProfile(ok: Bool) async throws -> String {
    let id = try await fetchNumber(from: ok)   // propagate on error
    return "id:\\(id)"
}

Task {
    do {
        let s = try await loadProfile(ok: true)
        print(s) // "id:7"
    } catch {
        print("propagated:", error)
    }
}

구체적인 오류 포착

enum FileError: Error { case notFound }

func mightCancel() async throws {
    for _ in 0..<5 {
        try Task.checkCancellation()                 // throws CancellationError
        try await Task.sleep(nanoseconds: 30_000_000)
    }
}

Task {
    let t = Task { try await mightCancel() }
    t.cancel()
    do {
        try await t.value
    } catch is CancellationError {
        print("cancelled cleanly")                   // handle cancellation separately
    } catch {
        print("other error:", error)
    }
}

지침

시도 후 기다리기를 사용한 오류 처리

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