Oracle PL/SQL Programming, Third Edition

Module Overloading

When more than one program in the same scope share the same name, the programs are said to be overloaded. PL/SQL supports the overloading of procedures and functions in the declaration section of a block (named or anonymous), package specifications and bodies, and object type definitions. Overloading is a very powerful concept, and you should exploit it fully to improve the usability of your software.

Here is a very simple example of three overloaded modules defined in the declaration section of an anonymous block (therefore, all are local modules):

DECLARE
   /* First version takes a DATE parameter. */
   FUNCTION value_ok (date_in IN DATE) RETURN BOOLEAN IS
   BEGIN
      RETURN date_in <= SYSDATE;
   END;

   /* Second version takes a NUMBER parameter. */
   FUNCTION value_ok (number_in IN NUMBER) RETURN BOOLEAN  IS
   BEGIN
      RETURN number_in > 0;
   END;

   /* Third version is a procedure! */
   PROCEDURE value_ok (number_in IN NUMBER) IS
   BEGIN
      IF number_in > 0 THEN 
         DBMS_OUTPUT.PUT_LINE (number_in || 'is OK!');
      ELSE
         DBMS_OUTPUT.PUT_LINE (number_in || 'is not OK!');
      END IF;
   END;

BEGIN

When the PL/SQL runtime engine encounters the following statement:

IF value_ok (SYSDATE) THEN ...

the actual parameter list is compared with the formal parameter lists of the various overloaded modules, searching for a match. If one is found, PL/SQL executes the code in the body of the program with the matching header.

Tip

Another name for overloading is static polymorphism . The term polymorphism refers to the ability ...