CRTP的静态多态性:使用基类调用派生方法 [英] Static Polymorphism with CRTP: Using the Base Class to Call Derived Methods

问题描述

C ++中virtual的主要优点之一是能够使用基类(指针或引用)来调用派生方法.

One of the main benefits of virtual in C++ is being able to use the base class (pointer or reference) to call derived methods.

我正在阅读使用CRTP实现静态多态性，但是我可以无法理解如何使用此技术来实现我上面提到的内容，因为当需要模板时，我无法将函数声明为类型为Base.

I'm reading up on using CRTP to implement static polymorphism, but I can't understand how to achieve what I've mentioned above using this technique, because I can't declare a function as taking type Base when this requires a template.

在我看来，只需使用函数重载就可以实现本文中描述的内容，因此，我敢肯定，这项技术还必须有更多的内容.

It seems to me that what is described in the article could be achieved by simply using function overloading, so I'm sure that there must be more to this technique.

(PS:在对

(PS: this exact problem is alluded to in a comment to an answer to this question, but unfortunately no one had replied to it: "What vtables truly provide is using the base class (pointer or reference) to call derived methods. You should show how it is done with CRTP here.")

这是我的最小代码，它给出错误在'&'标记之前缺少模板参数 void Print(Base& Object)".

Here is my minimal code, which gives the error "missing template arguments before ‘&’ token void Print(Base& Object)".

#include <cstring>
#include <iostream>

template <typename Derived>
struct Base
{
    std::string ToStringInterface() { return static_cast<Derived*>(this)->ToString(); }

    std::string ToString()  {   return "This is Base.";     }
};

struct Derived : Base<Derived>
{
    std::string ToString()  {   return "This is Derived.";  }
};

void Print(Base& Object)
{
    std::cout << Object->ToStringInterface() << std::endl;
}

int main()
{
    Derived MyDerived;

    // This works, but could have been achieved with a function overload.
    std::cout << MyDerived.ToStringInterface() << std::endl;

    // This does not work.
    Print(MyDerived);
}

推荐答案

好，您需要声明print一个模板函数:

Well, you need to declare print a template function :

template<class T>
void Print(Base<T>& Object)
{
    std::cout << Object.ToStringInterface() << std::endl;
}

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