swift-strict

Swift Strict Standard

Rules extracted from 3 production SwiftUI iOS apps.

CRITICAL: Unwrapping Rules

SW-01: Never force unwrap in production code

// BAD
let name = user!.name
let url = URL(string: urlString)!
let day = calendar.date(byAdding: .day, value: -1, to: date)!

// GOOD
guard let name = user?.name else { return }
guard let url = URL(string: urlString) else {
    throw AppError.invalidURL(urlString)
}
guard let day = calendar.date(byAdding: .day, value: -1, to: date) else { return }

Exceptions (very rare, must justify):

• fatalError() in required init?(coder:) for programmatic-only views
• @IBOutlet connections (but prefer programmatic UI)

SW-02: Use guard let for early returns, if let for scoped binding

// GOOD: guard for early exit (preferred pattern)
func listNotes(in folder: String) -> [Note] {
    guard let root = cloud.stikRoot else { return [] }
    guard let files = try? fm.contentsOfDirectory(at: root) else { return [] }
    return files.filter { ... }
}

// GOOD: if let when value only needed in branch
if let fileName = removed.photoFilename {
    let url = Self.photosDir.appendingPathComponent(fileName)
    try? fm.removeItem(at: url)
}

Default to guard. Use if-let only when the value is needed for one branch.

SW-03: Avoid try? for critical operations

// BAD: silently swallows error
try? FileManager.default.createDirectory(at: dir, withIntermediateDirectories: true)

// GOOD: handle or propagate
do {
    try FileManager.default.createDirectory(at: dir, withIntermediateDirectories: true)
} catch {
    logger.error("Failed to create directory: \(error)")
    throw AppError.fileSystemError(error)
}

// ACCEPTABLE: truly optional operations
try? fm.removeItem(at: tempFile) // Cleanup, failure is OK

CRITICAL: Error Handling

SW-04: Custom error enums with LocalizedError

enum AppError: LocalizedError {
    case invalidFolderName
    case containerUnavailable
    case networkUnavailable
    case unauthorized
    case serverError(Int)

    var errorDescription: String? {
        switch self {
        case .invalidFolderName: String(localized: "error_invalid_folder")
        case .containerUnavailable: String(localized: "error_container")
        case .networkUnavailable: String(localized: "error_network")
        case .unauthorized: String(localized: "error_unauthorized")
        case .serverError(let code): String(localized: "error_server \(code)")
        }
    }
}