nsCOMPtr<nsIPrinterEnumerator> printerEnumerator;  printerEnumerator = do_CreateInstance(kCPrinterEnumerator, &rv); if (NS_FAILED(rv)) return rv;
nsCOMPtr<nsIPrinterEnumerator> printerEnumerator = do_CreateInstance(kCPrinterEnumerator, &rv); NS_ENSURE_SUCCESS(rv, rv);
nsPrinterListEnumerator::Init(){  nsresult rv;  nsCOMPtr<nsIPrinterEnumerator> printerEnumerator;  printerEnumerator = do_CreateInstance(kCPrinterEnumerator, &rv);  if (NS_FAILED(rv))    return rv;  return printerEnumerator->EnumeratePrinters(&mCount, &mPrinters);}