Dynamic dispatch too dynamic!

Question

It seems that the dynamic dispatch feature in 9i is too dynamic.
Too dynamic because it's not possible to execute super methods
in an overridden method. In Java, the keyword "super" is used to
invoke the corresponding method on the super class, in C++ the
programmer can control which class' method is called by using
the class name.
I'm trying to accomplish this with PL/SQL. At OpenWorld 2000 it
was told that a keyword SUPER could be used to access the method
on the super class but I cannot find this in the documentation
and I've tried to invoke the given type's method directly, but
the dynamic dispatch goes into a recursive loop because it calls
the overridden method directly.
Some examples are in place here:
create or replace type person as object (
name varchar2(30),
address varchar2(100),
member function print return varchar2
) not final;
show errors
create or replace type body person as
member function print return varchar2 as
begin
return(/*super() ||*/ 'PERSON: { name = ''' || name ||
''', address = ''' || address || ''' }');
end;
end;
show errors
create or replace type student under person (
dept varchar2(30),
overriding member function print return varchar2
) not final;
show errors
create or replace type body student as
overriding member function print return varchar2 as
begin
return(/*super() ||*/ 'STUDENT: { dept = ' || dept || ' }');
end;
end;
show errors
create or replace type part_time_student under student (
numhrs number,
overriding member function print return varchar2
show errors
create or replace type body part_time_student as
overriding member function print return varchar2 as
begin
return(/*super() ||*/ 'PART_TIME_STUDENT: { numhrs = ' ||
numhrs || ' }');
end;
end;
show errors
create table persons of person;
insert into persons values (person('name', 'address'));
insert into persons values (student('name', 'address', 10));
insert into persons values (part_time_student('name', 'address',
10, 15));
select p.print()
from persons p;
In the PRINT method I would like to reuse the inherited method
by calling it and let it do it's work without me having to copy
the code to the overridden method. In other words, I would like
to be able to call it using SUPER() or something similar. But
SUPER isn't reckognized by the compiler so what should I use?
I've also tried to call the method directly, eg in
PART_TIME_STUDENT.PRINT call STUDENT.PRINT(SELF) but because the
dynamic dispatch is too dynamic this actually calls
PART_TIME_STUDENT.PRINT recursively -- endless loop :-(. I would
consider this as a bug because I tell the compiler exactly which
method I want to call, as opposed to O.PRINT where I invoke the
most specialized method on an object O.
How can this be done?
Thanks.
Finn Ellebaek Nielsen
ChangeGroup ApS

Answer 1

Finn,
It was an oversight, that 'super' didn't make it into the
release. The suggestd work around was to use the name of super
type explicitly as you have tried and failed.
Do you have a matalink customer id to file a iTAR? Let me know
if you don't have one.
Regards,
Geoff
It seems that the dynamic dispatch feature in 9i is too dynamic.
Too dynamic because it's not possible to execute super methods
in an overridden method. In Java, the keyword "super" is used to
invoke the corresponding method on the super class, in C++ the
programmer can control which class' method is called by using
the class name.
I'm trying to accomplish this with PL/SQL. At OpenWorld 2000 it
was told that a keyword SUPER could be used to access the method
on the super class but I cannot find this in the documentation
and I've tried to invoke the given type's method directly, but
the dynamic dispatch goes into a recursive loop because it calls
the overridden method directly.
Some examples are in place here:
create or replace type person as object (
name varchar2(30),
address varchar2(100),
member function print return varchar2
) not final;
show errors
create or replace type body person as
member function print return varchar2 as
begin
return(/*super() ||*/ 'PERSON: { name = ''' || name ||
''', address = ''' || address || ''' }');
end;
end;
show errors
create or replace type student under person (
dept varchar2(30),
overriding member function print return varchar2
) not final;
show errors
create or replace type body student as
overriding member function print return varchar2 as
begin
return(/*super() ||*/ 'STUDENT: { dept = ' || dept || ' }');
end;
end;
show errors
create or replace type part_time_student under student (
numhrs number,
overriding member function print return varchar2
show errors
create or replace type body part_time_student as
overriding member function print return varchar2 as
begin
return(/*super() ||*/ 'PART_TIME_STUDENT: { numhrs = ' ||
numhrs || ' }');
end;
end;
show errors
create table persons of person;
insert into persons values (person('name', 'address'));
insert into persons values (student('name', 'address', 10));
insert into persons values (part_time_student('name', 'address',
10, 15));
select p.print()
from persons p;
In the PRINT method I would like to reuse the inherited method
by calling it and let it do it's work without me having to copy
the code to the overridden method. In other words, I would like
to be able to call it using SUPER() or something similar. But
SUPER isn't reckognized by the compiler so what should I use?
I've also tried to call the method directly, eg in
PART_TIME_STUDENT.PRINT call STUDENT.PRINT(SELF) but because the
dynamic dispatch is too dynamic this actually calls
PART_TIME_STUDENT.PRINT recursively -- endless loop :-(. I would
consider this as a bug because I tell the compiler exactly which
method I want to call, as opposed to O.PRINT where I invoke the
most specialized method on an object O.
How can this be done?
Thanks.
Finn Ellebaek Nielsen
ChangeGroup ApS