问尝试打印错误描述(也称为ErrorType)枚举

EN

enum UpdateError: Error {
    case NoResults
    case UpdateInProgress
    case NoSubredditsEnabled
    case SetWallpaperError

    var description: String {
        switch self {
        case .NoResults:
            return "No results were found with the current size & aspect ratio constraints."
        case .UpdateInProgress:
            return "A wallpaper update was already in progress."
        case .NoSubredditsEnabled:
            return "No subreddits are enabled."
        case .SetWallpaperError:
            return "There was an error setting the wallpaper."
        }
    }

    // One of many nested enums
    enum JsonDownloadError: Error {
        case TimedOut
        case Offline
        case Unknown

        var description: String {
            switch self {
            case .TimedOut:
                return "The request for Reddit JSON data timed out."
            case .Offline:
                return "The request for Reddit JSON data failed because the network is offline."
            case .Unknown:
                return "The request for Reddit JSON data failed for an unknown reason."
            }
        }
    }

    // ...
}

do {
    try functionThatThrowsUpdateError()
} catch {
    NSLog((error as! UpdateError).description)
}