Dispatch-function resolution is the slowest, but most flexible, of the three method-resolution techniques. Dispatch functions permit method resolution to be based on arbitrary rules associated with the class of which the receiving object is an instance. Thus, a class implementor has complete freedom in determining how methods invoked on its instances are resolved.
With both offset and name-lookup resolution, the net effect is the same-the method procedure that is ultimately selected is the one supported by the class of which the receiver is an instance. For example, if the receiver is an instance of class "Dog", then Dog's method procedure will be selected; but if the receiver is an instance of class "BigDog", then BigDog's method procedure will be selected.
By contrast, dispatch-function resolution allows a class of instances to be defined such that the method procedure is selected using some other criteria. For example, the method procedure could be selected on the basis of the arguments to the method call, rather than on the receiver. For more information on dispatch-function resolution, see the description and examples for the somDispatch and somOverrideMTab methods in the SOMobjects Developer Toolkit: Programmers Reference Manual.