How do you convert an iPhone OSStatus code to something useful?

Question

I am getting more than a little sick of this iPhone SDK and its documentation...

I am calling AudioConverterNew

in the documentation under Returns: it says \

Answer 1

For iOS 11.3+, I'm using an extension on OSStatus…

extension OSStatus {

    var error: NSError? {
        guard self != errSecSuccess else { return nil }

        let message = SecCopyErrorMessageString(self, nil) as String? ?? "Unknown error"

        return NSError(domain: NSOSStatusErrorDomain, code: Int(self), userInfo: [
            NSLocalizedDescriptionKey: message])
    }
}

which you can call like…

let status = SecItemAdd(attributes as CFDictionary, nil)

if let error = status.error {
    throw error
}    
// etc

Having written this I noticed this is very close to @RomanMykitchak's earlier answer (so please give him the upvote) - but I'll leave it here as the extension might prove useful to someone.