c++ - 模板特化继承自特定的子类

Question

class Base { ... };
class Derived1 : Base { ... };
class Derived2 : Base { ... };

template <> class BaseDecorator<Base> : **SpecificDerived** { ... };

SpecificDerived 是否可以引用正在使用的特定派生类？这样

BaseDecorator<Derived1> bd-d1;

会实例化一个继承自 Derived1 的 BaseDecorator 吗？

出现这个问题是因为我需要为一个库类及其所有派生类提供一个装饰器，但又想让代码尽可能干。

谢谢!

Answer 1

如果我对你的问题的理解正确，你希望你的 BaseDecorator 继承自特定的 Derived 类。

如果是这样的话，你可以这样做:

#include <iostream>
#include <type_traits>

class Base {
    public:
    virtual void f1() {
        std::cout << "Base::f1" << std::endl;   
    }
};

class Derived1 : public Base {
    public:
    void f1() override {
        std::cout << "Derived1::f1" << std::endl;   
    }
};

class Derived2 : public Base {
    public:
    void f1() override {
        std::cout << "Derived2::f1" << std::endl;   
    }
};

class Derived3 {
    public:
    void f1() {
        std::cout << "Derived3::f1" << std::endl;   
    }
};

template <typename T,
          typename = typename std::enable_if<std::is_base_of<Base, T>::value>::type >
class BaseDecorator;

template <typename T>
class BaseDecorator<T>: public T {
    public:
    void f2() {
        T::f1();
    }
};

int main() {
    BaseDecorator<Derived1> bd1;
    bd1.f2();

    BaseDecorator<Derived2> bd2;
    bd2.f2();

    //BaseDecorator<Derived3> bd3; // Compilation fails !!!
    //bd3.f2(); // Compilation fails !!!

    return 0;   
}

输出:

Derived1::f1
Derived1::f2