More Effective C++ 条款33 将非尾端(non-leaf classes)设计为抽象类(abstract classes)

1. 假如程序有一个Chicken class,Lizard class,Animal class,其中Chicken class和Lizard class继承自Animal class,整个继承体系像这样:

    Animal负责具体化所有东吴的共同特征,Lizard和Chicken是需要特殊对待的两种动物,它们的简化定义像这样:

class Animal {
public:
    Animal& operator=(const Animal& rhs);
    ...
};
class Lizard: public Animal {
public:
    Lizard& operator=(const Lizard& rhs);
    ...
};
class Chicken: public Animal {
public:
    Chicken& operator=(const Chicken& rhs);
    ...
};

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