Idealized Image of Inheritance

Much of the power of object-oriented techniques will come about from a purposeful confusion between a parent and child class, and the ability to substitute an instance of a child class where we are expecting an instance of the parent class. We call this the principle of substitutability.

To see why the principle of substitutability should be valid, consider the following argument:

Intro OOP, Chapter 7, Slide 6
[audio] [real] Text to accompany slide6, in Chapter 7 of An Introduction to Object-Oriented Programming