带有附加模板参数的可变CRTP基类

#include <iostream>

// 基类模板，接受派生类类型和其他模板参数
template <typename Derived, typename Policy>
class Base {
public:
    void interface() {
        // 调用派生类的实现
        static_cast<Derived*>(this)->implementation();
        
        // 使用附加模板参数
        Policy::apply();
    }
};

// 策略类模板
template <typename T>
struct Policy {
    static void apply() {
        std::cout << "Default policy applied." << std::endl;
    }
};

// 派生类
class Derived : public Base<Derived, Policy<int>> {
public:
    void implementation() {
        std::cout << "Derived class implementation." << std::endl;
    }
};

// 自定义策略类
template <>
struct Policy<int> {
    static void apply() {
        std::cout << "Custom policy for int applied." << std::endl;
    }
};

int main() {
    Derived d;
    d.interface();
    return 0;
}

class WrongDerived : public Base<WrongDerived> { // 缺少附加模板参数
public:
    void implementation() {
        std::cout << "WrongDerived class implementation." << std::endl;
    }
};

class CorrectDerived : public Base<CorrectDerived, Policy<int>> { // 添加正确的附加模板参数
public:
    void implementation() {
        std::cout << "CorrectDerived class implementation." << std::endl;
    }
};