sS withStringBuilder(IVF1<StringBuilder> f) {
  new StringBuilder buf;
  if (f != null) f.get(buf);
  ret str(buf);
}

sS withStringBuilder(int expectedLength, IVF1<StringBuilder> f) {
  StringBuilder buf = new(expectedLength);
  if (f != null) f.get(buf);
  ret str(buf);
}