I am convinced that this is not just a programmer's mistake. This is an illustration of the problem with the paradigm itself. Inheritance makes you want to gl

I am convinced that this is not just a programmer's mistake. This is an illustration of the problem with the paradigm itself. Inheritance makes you want to glue unrelated things together. Inheritance views the world as fundamentally hierarchical; you can divide things up into branches of a tree. A node on the tree either has all of a set of functions or none of them. Any code you put into Reptile will never be needed by a Mammal, and will never be inappropriate for an object that needs other things in Reptile. But of course, that's unrealistic. Where would you put swim()? Where would you put fly()? Code reuse can't always be decomposed into a tree. And in an inheritance paradigm, you get ugly workarounds in that case -- cut and pasted code, nasty multiple inheritance hacks, or util classes. All bad things. What you want are things coupled, not by convenient proximity in current function, but by logical relationship. You want a class that has swimming-related code and nothing else, that any swimmer can use without preconceptions about whether it's a Reptile or a Mammal. You want, in short, Traits.