do/catch और त्रुटियाँ परिभाषित करना (enum)

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")

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)
}

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)
}

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)")