Custom listagg function using cursor to bypass ORA-01489

When using build-in listagg function one should always consider that resulting string must have a length less or equal to 4000 characters. If does exceed then an error 'SQL Error: ORA-01489: result of string concatenation is too long' is thrown.
Here's a package implementing a custom aggregate function that bypasses this restriction.

create or replace PACKAGE "PK_UTILS" AS

type ref_cur is ref cursor;

function LISTAGG_CLOB( a_cur in pk_utils.ref_cur, a_delimiter in varchar2 ) return clob;

END PK_UTILS;
/
create or replace PACKAGE BODY "PK_UTILS" AS

function listagg_clob( a_cur in pk_utils.ref_cur, a_delimiter in varchar2 ) return clob
as
  v_single_value clob;
  v_result clob; 
begin
  fetch a_cur into v_single_value;
  if ( a_cur%NOTFOUND ) then
    goto FIN;
  end if;
  v_result := v_single_value;
  loop
    fetch a_cur into v_single_value;
    exit when a_cur%NOTFOUND;
    v_result := v_result || a_delimiter || v_single_value;
  end loop;
<<FIN>>
  return v_result;
end;

END PK_UTILS;
/

And here is a small user test emulating 'within group (order by ...)' functionality.

with prepared as (
  select 1 a, 1 b from dual 
  union all
  select 2 a, 2 b from dual 
  union all
  select 3 a, 1 b from dual 
  union all
  select 4 a, 2 b from dual 
)
select q.b
  , pk_utils.listagg_clob( cursor( select a from prepared where b = q.b order by a desc ) , ',' ) 
from ( 
  select b 
  from prepared
  group by b 
) q
;/

         B LISTAGG_
---------- ------------------
         1 3,1               
         2 4,2