Many, many programmers don't really understand inheritance, and that fact is terrible. Many who don't understand inheritance think they do, and therefore believ

Many, many programmers don't really understand inheritance, and that fact is terrible. Many who don't understand inheritance think they do, and therefore believe that their bad designs are characteristic of all designs, and that misunderstanding is terrible. Terrible inheritance is terrible. Good inheritance is good. To enjoy good inheritance, first learn to think in layers of abstraction. If this is hard for you (it's not easy for anyone), either train yourself to do it or don't use inheritance—but then don't criticize inheritance for your own shortcomings. Second, make each class properly express its proper abstraction. Abstract things like "items" should be very abstract. They might have a price but have no idea how price is calculated. More concrete things like books and movies should have more concreteness, but no more than necessary. Often, "deep" layers of abstraction really are little more than interfaces. All the major languages have ways of expressing interfaces as distinct from classes as such, but there is no distinction between them at heart: an "interface" is just a very abstract class; that is, it offers methods without (or with few) implementations. Whether you use "interfaces" or "protocols" or "abstract classes", your language probably offers ways of expressing "lots of abstraction" as well as ways of expressing "more concreteness". Think in layers of abstraction and then use all the tools available to express that thinking directly. When requirements, or insights into the design should work, change, then naturally anything can change, from interfaces to detailed implementations. No tool, language, or technique will prevent change, but a clear mental model of what is being expressed and code that succinctly and directly expresses that mental model is your best basis for coping with change. Don't blame inheritance. Don't, for crying out loud, praise interfaces when they are simply a purified form of abstract inheritance. Learn to use the tools that have served millions of programmers well for twenty or thirty years and then the tools won't seem so dangerous and strange. Or, if the tools really just don't suit your way of thinking, don't use them; use other tools; but either way don't blame the tools.