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copied!<p>Is inheritance really needed? Depends what you mean by "really". You could go back to punch cards or flicking toggle switches in theory, but it's a terrible way to develop software.</p> <p>In procedural languages, yes, class inheritance is a definite boon. It gives you a way to elegantly organise your code in certain circumstances. It should not be overused, as any other feature should not be overused. </p> <p>For example, take the case of digiarnie in this thread. He/she uses interfaces for nearly everything, which is just as bad as (possibly worse than) using lots of inheritance.</p> <p>Some of his points :</p> <blockquote> <p>this helps with testing and improves readability </p> </blockquote> <p>It doesn't do either thing. You never actually test an interface, you always test an object, that is, an instantiation of a class. And having to look at a completely different bit of code helps you understand the structure of a class? I don't think so.</p> <p>Ditto for deep inheritance hierarchies though. You ideally want to look in one place only.</p> <blockquote> <p>Using interfaces, I would get the same effect but I would mimic inheritance by using 'delegation'.</p> </blockquote> <p>Delegation is a very good idea, and should often be used instead of inheritance (for example, the Strategy pattern is all about doing exactly this). But interfaces have zero to do with delegation, because you cannot specify any behaviour at all in an interface.</p> <blockquote> <p>also makes refactoring a whole lot easier.</p> </blockquote> <p>Early commitment to interfaces usually makes refactoring harder, not easier, because there are then more places to change. Overusing inheritance early is better (well, less bad) than overusing interfaces, as pulling out delegate classes is easier if the classes being modified do not implement any interfaces. And it's quite often from those delegates than you get useful interfaces.</p> <p>So overuse of inheritance is a bad thing. Overuse of interfaces is a bad thing. And ideally, a class will neither inherit from anything (except maybe "object" or the language equivalent), nor implement any interfaces. But that doesn't mean either feature should be removed from a language.</p>

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