interface BitIO {
  replace ByteHead with BitHead.
  
  void readWrite(ByteHead head);
  
  default byte[] saveToByteArray aka saveAsByteArray() {
    var baos = byteArrayOutputStream();
    readWrite(new ByteHead(baos));
    ret baos.toByteArray();
  }
  
  default File saveToFile(File file) {
    temp OutputStream out = bufferedFileOutputStream(file);
    readWrite(new ByteHead(out));
    ret file;
  }
  
  default selfType load(byte[] data) {
    readWrite(new ByteHead(new ByteArrayInputStream(data)));
    this;
  }
  
  default selfType load(File file) {
    temp InputStream in = bufferedInputStream(file);
    readWrite(new ByteHead(in));
    this;
  }
}