@Override
  public SelLong field(SelString field) {
    String fieldName = field.getInternalVal();
    if ("length".equals(fieldName)) {
      return SelLong.of(val.length);
    }
    throw new UnsupportedOperationException(type() + " DO NOT support accessing field: " + field);
  }
@Test
  public void field() {
    SelLong res = one.field(SelString.of("length"));
    assertEquals(2, res.longVal());
  }