SQL & PL/SQL :: Get The Distinct Elements Of A Collection Of Objects

I have a collection of objects built in a PL/SQL program.

I want to keep only the distinct elements of this collection for the rest of the program.

I failed to find the correct way to do it

For instance (the actual object is far more complex containing object attributes itself), with the following types:

drop type t1b
/
drop type t1a
/
create or replace type t1a as object (
v1 integer,
v2 integer
)
/
create or replace type t1b as table of t1a
/
I have the following variable:

v t1b := t1b(t1a(1,2),t1a(1,2));

And I want to get only one "t1a(1,2)" in my collection.

My first idea (actually the second one but it does not matter) was to use DISTINCT:

SQL> declare

2 v t1b := t1b(t1a(1,2),t1a(1,2));
3 begin
4 select distinct t1a(v1,v2) bulk collect into v from table(v);
5 dbms_output.put_line(v.count);
6 end;
7 /
declare
*
ERROR at line 1:

ORA-22950: cannot ORDER objects without MAP or ORDER method ORA-06512: at line 4

As I said the object is far more complex and builting a MAP function is quite tedious (but I will do it if there is no other way).

The next idea was to use multiset operators:

SQL> declare
2 v t1b := t1b(t1a(1,2),t1a(1,2));
3 begin
4 select v multiset intersect distinct v into v from dual;
5 dbms_output.put_line(v.count);
6 end;
7 /
1

PL/SQL procedure successfully completed.

This works well but I suspect this is not the correct way and there is one to do it in PL/SQL but currently failed to find it.