// CompletionClosure uses Swift's Result type:
// - .success(Void): Operation succeeded
// - .failure(ErrorInfo): Operation failed
func someAsyncOperation(completion: @escaping CompletionClosure) {
    // Async operation...
}
someAsyncOperation { result in
    switch result {
    case .success:
        print("Operation succeeded")
    case .failure(let error):
        print("Error code: \\(error.code), message: \\(error.message)")
    }
}