SQL & PL/SQL

I am using a table function in Oracle 8.1.7.4.0. I did declare an object type and a collection type like this:

CREATE TYPE t_obj AS OBJECT ...
CREATE TYPE t_tab AS TABLE OF t_obj;

My table function returns t_tab and is called like this:

SELECT ... FROM TABLE (CAST (my_pkg.table_fnc AS t_tab)) ...

This works pretty well as long as I run it in the same schema that owns the function and the 2 types. As soon as I run this query from another schema, I get an ORA-22905: cannot access rows from a non-nested table item error, even though I granted execute on both the types and the function to the other user and I created public synonyms for all 3 objects.

As soon as I specify the schema name of t_tab in the cast, the query runs fine:

SELECT ... FROM TABLE (CAST (my_pkg.table_fnc AS owner.t_tab)) ...

I don't like to have a schema hard coded in a query, therefore I'd like to do this without the schema. Any ideas of how to get around this error?