sclass NotifyingStringBufferRotator implements Runnable {
  NotifyingStringBuffer buf;
  IF0<Int> getMaxChars;
  
  *(NotifyingStringBuffer *buf, IF0<Int> *getMaxChars) {}
  
  run {
    Int max = callF(getMaxChars);
    if (max == null || buf.length() <= max) ret;
     
    try {
      int newLength = max/2;
      int ofs = buf.length()-newLength;
      S newString = buf.substring(ofs);
      buf.setLength(0);
      buf.append("[...] ").append(newString);
    } catch (Exception e) {
      buf.setLength(0);
    }
    buf.trimToSize();
  }
}

svoid makeNotifyingStringBufferRotate(NotifyingStringBuffer buf, IF0<Int> getMaxChars) {
  if (hasElementWithClassShortNamed('NotifyingStringBufferRotator, buf.onChange)) ret;
  buf.onChange(new NotifyingStringBufferRotator(buf, getMaxChars));
}