create or replace
function f
         (pin_input pls_integer)
         return sys_refcursor is
   rc sys_refcursor;
begin
   if pin_input = 1
   then
      open rc for
         select 'a', 'b', 'c'
           from dual;
   else
      open rc for
         select 'x', 'y', 'z'
           from dual;
   end if;
   --
   return rc;
end f;

declare
   c integer := dbms_sql.open_cursor;
   rc sys_refcursor;
begin
   dbms_sql.parse
      (c             => c
      ,statement     => 'f (2)'
      ,language_flag => dbms_sql.native
      );
   --
   dbms_sql.close_cursor (c => c);
exception
   when others then
      if dbms_sql.is_open (c => c)
      then
         dbms_sql.close_cursor (c => c);
      end if;
      --
      raise;
end;

SQL> var rc refcursor
SQL> create function f
  2  return sys_refcursor
  3  is
  4   rc sys_refcursor;
  5  begin
  6   open rc for 'select ename from emp';
  7   return rc;
  8  end;
  9  /

Function created.

SQL> exec :rc := f

PL/SQL procedure successfully completed.

SQL> print rc

ENAME
----------
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING
TURNER
ADAMS

ENAME
----------
JAMES
FORD
MILLER

14 rows selected.