错误:模板可能不是“虚拟"的 [英] error: templates may not be 'virtual'

问题描述

我希望能够为基类MCFormater提供一种适用于不同类型(uint32，uint8 ...)的格式化方法

I would like to be able to provide to the base class MCFormater a formatting method that would work for different types (uint32, uint8...)

class MCFormater {
    public:
    MCFormater() {}
    virtual ~MCFormater() {}
    virtual mcc_t Gen();
protected:
    template<typename K>                          //here is the problem
    virtual void Format(K& a, const K& b) = 0; 
    //...
    uint32_t a;
    uint8_t b;
    void Foo();
};

void MCFormater::Foo() {
   Format<uint32_t>(a, 3);     //I want to be able to call for Format
   Format<uint8_t>(b, 3);      //with uint32_t, and uint8_t, and more 
}


class GFormater : public MCFormater {
    GFormater() {}
    template<typename K>
    virtual void Format(K& a, const K& b) {
        a = b;
    }
};

class EFormater : public MCFormater {
    EFormater() {} 
    template<typename K>
    virtual void Format(K& a, const K& b) {
        a |= b;
    }
};

但是我得到了错误:模板可能不是虚拟"的.正确的方法是什么?(有吗?)

but I get the error: templates may not be 'virtual'. what is the right way to do it? (is there one?)

推荐答案

修改...

class MCFormater {
    public:
    MCFormater() {}
    virtual ~MCFormater() {}
    virtual mcc_t Gen();
protected:
    template<typename K>                          //here is the problem
    virtual void Format(K& a, const K& b) = 0; 
    //...
    uint32_t a;
    uint8_t b;
    void Foo();
};

void MCFormater::Foo() {
   Format<uint32_t>(a, 3);
   Format<uint8_t>(b, 3);
}


class GFormater : public MCFormater {
    GFormater() {}
    template<typename K>
    virtual void Format(K& a, const K& b) {
        a = b;
    }
};

class EFormater : public MCFormater {
    EFormater(FTEKeeps* keeps) : MCFormater(keeps) {} 
    template<typename K>
    virtual void Format(K& a, const K& b) {
        a |= b;
    }
};

致...

#include<iostream>

using namespace std;

template<typename K>
class MCFormater {
public:
    MCFormater() {}
    virtual ~MCFormater() {}
    virtual mcc_t Gen();
protected:  
    virtual void Format(K& a, const K& b) = 0;
    //...
    uint32_t a;
    uint8_t b;
    void Foo();
};

template<typename K>
void MCFormater<K>::Foo() {
    Format<uint32_t>(a, 3);
    Format<uint8_t>(b, 3);
}

template<typename K>
class GFormater : public MCFormater<K> {
    GFormater() {}  
    virtual void Format(K& a, const K& b) {
        a = b;
    }
};

template<typename K>
class EFormater : public MCFormater<K> {
    EFormater(FTEKeeps* keeps) : MCFormater<K>(keeps) {}    
    virtual void Format(K& a, const K& b) {
        a |= b;
    }
};

说明:成员函数模板不能是虚拟的.如果允许这样做，则每次使用不同类型的Format函数调用时，链接器都必须向虚拟表中添加一个新条目.动态链接会让人难以接受.

Explanation: Member function templates cannot be virtual. If this was allowed then the linker would have to add a new entry to the virtual table every time the Format function was called with a different type. Dynamic linking would be unacceptably complicated.

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