do/catch와 오류 정의(열거형)

개요

오류 열거형

enum FileError: Error {
    case notFound(path: String)
    case unreadable(path: String)
    case corrupted
}
print("Defined FileError enum")

오류 발생 기초

func loadText(from path: String) throws -> String {
    if path.isEmpty { throw FileError.notFound(path: "(empty)") }
    if !path.hasSuffix(".txt") { throw FileError.unreadable(path: path) }
    return "Contents of " + path
}
print("Ready to throw on bad input")

구체적인 오류 포착

do {
    let text = try loadText(from: "notes.txt")
    print(text)
} catch FileError.notFound(let p) {
    print("Missing file at:", p)
} catch FileError.unreadable(let p) {
    print("Cannot read:", p)
} catch {
    print("Other error:", error)
}

catch let 및 switch

do {
    _ = try loadText(from: "")
} catch let error as FileError {
    switch error {
    case .notFound(let p): print("not found:", p)
    case .unreadable(let p): print("unreadable:", p)
    case .corrupted: print("file corrupted")
    }
} catch {
    print("unexpected:", error.localizedDescription)
}

복구와 재발생

func mustLoad(_ path: String) throws -> String {
    do {
        return try loadText(from: path)
    } catch FileError.notFound {
        // simple recovery: default content
        return "New file template"
    } catch {
        // escalate unknown issues
        throw error
    }
}
print(try? mustLoad("report.txt") ?? "(nil)")

사용자 지정 오류 패턴 확인

복습