Adding a Method to the System

 

Adding and removing methods are basic operations in an object-oriented environment. They are defined on class Root, therefore they can be invoked on every class via inheritance.

To add a new method to the system call

   (METHOD * ) GRAPE(class, "add-method")(name, func)

CLASS * class
char * name
void *(* func)()

This will add a new method to the method list of class class. The method is called name, func is the pointer to the function which implements the new method. The return value of "add-method" is the pointer to the structure of the new method, it should only be used to check if the method was successfully added. If the method couldn't be added (maybe there was already a method called name), an error message will be printed and "add-method" returns NULL.

By calling

   GRAPE(class, "delete-method")(name)

CLASS * class
char * name

the method name can be removed from the method list of class class, and with

   (METHOD * ) GRAPE(class/inst, "find-method")(name)

CLASS * class
INSTANCE * inst
char * name

it can be tested if a method named name exists on class class resp. on the class of the instance inst (of course the superclasses are also searched if necessary). The methods return a NULL pointer if the method wasn't found.