why this simple programm creates an end-of-file on communicatoin channel error - oracle

Question

CREATE OR REPLACE TYPE a IS OBJECT
(
b integer,
c varchar2(10)
);
/
declare
cursor ca return a is select 1,'e' from dual;
va a;
begin
null;
for cur in ca
loop
DBMS_OUTPUT.PUT_LINE('do nothing');
end loop;
end;
ORA-03113: end-of-file on communication channel
Process ID: 803778
Session ID: 64 Serial number: 4181
the loop as only one element and fast nothing is done in the loop.
But I get the error end-of-file communication channel
As #littlefoot said it works fine if I use a record defined in a package or no record at all. I don't know why it doesn't work with an object
code

Answer 1

Simply put, you can't do that.
Oracle does not support returning object types from a cursor. Cursors *always* return a rowtype. So to do something similar to what you want, you can define a table which has a column of the object type you're interested in, and then have the cursor return the rowtype of that table - i.e. something like:
CREATE OR REPLACE TYPE a IS OBJECT
(
b integer,
c varchar2(10)
);
CREATE TABLE tt
(t_a a);
INSERT INTO tt VALUES (a(1, 'e'));
declare
cursor ca return tt%ROWTYPE is select t_a from tt;
an_a a;
begin
FOR aRow IN ca LOOP
an_a := aRow.t_a;
dbms_output.put_line('an_a.b=' || an_a.b);
dbms_output.put_line('an_a.c=''' || an_a.c || '''');
end loop;
end;
db<>fiddle here

Answer 2

You never said what a is.
Documentation says that - if you use return clause, then it returns rowtype.
RETURN: Specifies the datatype of a cursor return value. You can use the %ROWTYPE attribute in the RETURN clause to provide a record type that represents a row in a database table or a row returned by a previously declared cursor. Also, you can use the %TYPE attribute to provide the datatype of a previously declared record.
A cursor body must have a SELECT statement and the same RETURN clause as its corresponding cursor spec. Also, the number, order, and datatypes of select items in the SELECT clause must match the RETURN clause.
ROWTYPE: A record type that represents a row in a database table or a row fetched from a previously declared cursor or cursor variable. Fields in the record and corresponding columns in the row have the same names and datatypes.
So, if your code were like this, it would work:
SQL> set serveroutput on
SQL>
SQL> declare
2 type a is record(val1 number, val2 varchar2(10));
3
4 cursor ca return a is select 1 ,'e' from dual;
5 va a;
6 begin
7 for cur in ca
8 loop
9 DBMS_OUTPUT.PUT_LINE(cur.val1 ||', '|| cur.val2 ||', do nothing');
10 end loop;
11 end;
12 /
1, e, do nothing
PL/SQL procedure successfully completed.
SQL>
Or, simpler, if you remove the return clause from your own code, it would also work:
SQL> declare
2 cursor ca --return a
3 is select 1,'e' from dual;
4 va a;
5 begin
6 null;
7 for cur in ca
8 loop
9 DBMS_OUTPUT.PUT_LINE('do nothing');
10 end loop;
11 end;
12 /
do nothing
PL/SQL procedure successfully completed.
SQL>
If you're asking what's the reason of end-of-file on communication channel, I wouldn't know.