How do I update a Nested Table of inherited Object Types?

Question

Does anyone know why the following line (commented out) doesn't work and what I can do? Is there some way to cast the column I am trying to update? I think I am going crazy....
create or replace type person_ot as object (name varchar2(10)) not final;
create or replace type student_ot under person_ot (s_num number) not final;
create type person_tt as table of person_ot;
declare
lv_person_list person_tt;
lv_sql varchar2(1000);
ref_cur sys_refcursor;
begin
lv_sql:= 'select new student_ot(''fred'', 100) from dual
union all
select new student_ot(''sally'', 200) from dual';
open ref_cur for lv_sql;
fetch ref_cur bulk collect into lv_person_list;
close ref_cur;
dbms_output.put_line(lv_person_list.count);
for i in lv_person_list.first..lv_person_list.last loop
lv_person_list(i).name := initcap(lv_person_list(i).name ); -- This works!
lv_person_list(i).s_num := 9999;  Why doesn't this line work and how can I update the column s_num ??? :-(
end loop;
end;
/

Answer 1

Hi Tubby - You are right...It would make sense to create the Type as type of student_ot. Only problem is I am trying to keep it generic. I will include full listing to show what I am doing...
create or replace type person_ot as object (name varchar2(10)) not final;
create or replace type student_ot under person_ot (s_num number) not final;
create type person_tt as table of person_ot;
create table persons of person_ot;
declare
lv_person_list person_tt;
lv_sql varchar2(1000);
ref_cur sys_refcursor;
begin
lv_sql:= 'select new student_ot(''fred'', 100) from dual
union all
select new student_ot(''sally'', 200) from dual';
open ref_cur for lv_sql;
fetch ref_cur bulk collect into lv_person_list;
close ref_cur;
for i in lv_person_list.first..lv_person_list.last loop
lv_person_list(i).name := initcap(lv_person_list(i).name );
lv_person_list(i).s_num := 9999;*                             Why doesn't this line work?? :-(
end loop;
forall i in lv_person_list.first..lv_person_list.last
insert into persons values lv_person_list(i);
end;
/