10.1. Why No Multiple Inheritance?

Scala, like Java, does not allow a class to inherit from multiple superclasses. At first, this seems like an unfortunate restriction. Why shouldn’t a class extend multiple classes? Some programming languages, in particular C++, allow multiple inheritance—but at a surprisingly high cost.

Multiple inheritance works fine when you combine classes that have nothing in common. But if these classes have common methods or fields, thorny issues come up. Here is a typical example. A teaching assistant is a student and also an employee: