Multiple Inheritance

In the Shape class hierarchy, we’ve seen single inheritance, where each class (except the root) has one and only one superclass, though a class can have multiple subclasses. Consider this alternative hierarchy:

A Rectangle is defined as a Quadrilateral with four right (90°) angles, while a Rhombus is a Quadrilateral with four equal sides. A Square has four right angles and four equal sides, so it inherits the properties of both a Rectangle and a Rhombus. This is an example of multiple inheritance. C++ permits multiple inheritance in addition to single inheritance, and it gives a lot of flexibility in coding, as it more accurately models many real-world situations.

Multiple inheritance has one major drawback: when a class inherits members with the same name from two different classes, how do you figure out which one to use? Resolving this apparently simple problem can actually be such a nightmare that many OOPLs, like Smalltalk and Java, decide that it’s simply not worth the hassle (Gallagher 1990; Sutherland 1995; Wyant 1995).