An Object and its Dispatch Table

The additional pointer in an object is known as the isa link. This picture shows an object and its isa link pointing the table for a class. Each class contains a pointer to the table for its parent class, and so on.

If a search fails to find a matching method for a message, a run-time error is reported.

[audio] [real] Text to accompany slide11, in Chapter 21 of An Introduction to Object-Oriented Programming