The problem which I am facing is similar to that presented in the original question. I have created a table of records, which I want to populate manually. I am facing several problems doing so. I cannot seem to find a suitable solution in any of the Oracle Docs or in this site, which may solve my problem.

The code is given below :
DECLARE

    TYPE my_rec IS RECORD (
       object_name         user_objects.object_name%type,
       object_type         user_objects.object_type%type,
       tablespace          user_tablespaces.tablespace_name%type,
       num_rows            NUMBER
    );

    TYPE my_array IS TABLE OF my_rec INDEX BY BINARY_INTEGER;

    my_table my_array ;
    l_row integer;

    function insert_data(
                 p_object_name     varchar2,
                 p_object_type     varchar2,
                 p_tablespace      varchar2,
                 p_num_rows        number
              )
    return integer
    is
        l_last_row integer;
        l_my_rec my_rec;
    begin
        my_table.extend;
        l_last_row := my_table.last_row;
        my_table(l_last_row).object_name  := p_object_name;
        my_table(l_last_row).object_type  := p_object_type;
        my_table(l_last_row).tablespace  := p_tablespace;
        my_table(l_last_row).num_rows  := p_num_rows;
        return l_last_row;
    end;

BEGIN

   l_row := insert_data('TABLE','TABLE1','TS1',340);
   l_row := insert_data('TABLE','TABLE2','TS1',640);
   l_row := insert_data('INDEX','INDEX1','TS2',340);

   for x in my_table.first .. my_table.last
   loop
       dbms_output.put_line(my_table(x).object_name||','||my_table(x).object_type||','||my_table(x).tablespace||','||to_char(my_table(x).num_rows));
   end loop;
END;
/

When I run the above code, it gives the following error :
SQL> @my_space.sql
        my_table.extend;
        *
ERROR at line 26:
ORA-06550: line 26, column 9:
PLS-00306: wrong number or types of arguments in call to 'EXTEND'
ORA-06550: line 26, column 9:
PL/SQL: Statement ignored
ORA-06550: line 27, column 25:
PLS-00302: component 'LAST_ROW' must be declared
ORA-06550: line 27, column 2:
PL/SQL: Statement ignored

I tried to initialize my_table at the place of declaration as shown below :

    my_table my_array := my_array();

But that gives me the following error :
PLS-00222: no function with name 'MY_ARRAY' exists in this scope

Any ideas what I am doing wrong.

Also I was wondering based on the answer to the main question that it is not possible to do it this way in PL/SQL. Correct me if I am wrong.

CREATE OR REPLACE PACKAGE pkg_test
IS
 TYPE myrec IS RECORD ( FIELD1 VARCHAR2( 30 ), OPERAND VARCHAR2( 1 ), FIELD2 VARCHAR2( 30 ) );
 TYPE mytab IS TABLE OF myrec INDEX BY PLS_INTEGER;
END;

DECLARE
 rec pkg_test.mytab; -- Seems it can see here
BEGIN
    rec(1) := pkg_test.mytab('A','=','B'); -- does not work: PLS0222, cannot see it anymore and consider mytab as a function (instead of a user type)
    rec(1).FIELD1 := 'A'; -- ...and so on, works
END;

create type my_rec as record(cost number(5),course_name varchar2(10));
create type my_tab as table of my_rec;
create table Tab_1(s_name varchar(10),cost_course my_tab)nested table cost_course store as course_tab;