Understanding Classical Inheritance

The idea of inheritance may seem complicated but as with all complexity, there’s a simplifying abstraction. Inheritance is, at its core, a mechanism for automatic message delegation. It defines a forwarding path for not-understood messages. It creates relationships such that, if one object cannot respond to a received message, it delegates that message to another. You don’t have to write code to explicitly delegate the message, instead you define an inheritance relationship between two objects and the forwarding happens automatically.

In classical inheritance these relationships are defined by creating subclasses. Messages are forwarded from subclass to superclass; the shared code is defined in the class hierarchy.