CRTP 奇异递归模板模式

#include <iostream>template <typename Derived>struct Base {    Derived&self()    {        return static_cast<Derived&>(*this);    }    const Derived&self() const    {        return static_cast<const Derived&>(*this);    }public:    void start()    {        self().run();    }};class Derived : public Base<Derived> {    friend Base<Derived>;    void run()    {        std::cout << "Derived run()" << std::endl;    }};

父类调用子类, 不过不同的 Base<Derived> 是不同的类, 好像没什么用处