public interface TXRDocIface {
  public abstract string gen ();
}

public class TXRDoc : TXRObject {
  public int doc_field;

  public override void copy (TXRObject copy) {
      stdout.printf ("TXRDoc:copy() called\n");
      if (copy is TXRObject) {
          base.copy (copy);
          ((TXRDoc)copy).doc_field = this.doc_field;
      }
  }
}