class FileIOException implements Exception {
  const FileIOException([String this.message = "",
                         OSError this.osError = null]);
  String toString() {
    StringBuffer sb = new StringBuffer();
    sb.add("FileIOException");
    if (!message.isEmpty()) {
      sb.add(": $message");
      if (osError != null) {
        sb.add(" ($osError)");
      }
    } else if (osError != null) {
      sb.add(": osError");
    }
    return sb.toString();
  }
  final String message;
  final OSError osError;
}