在C ++的子类中重载枚举 [英] Overloading an enum in a child class in c++

问题描述

我对定义要继承的通用类感兴趣，该通用类基于枚举和该枚举到某些数据结构的映射而有所不同。

I'm interested in defining a general class to be inherited that operates differently based on an enum and map of that enum to some data structure.

我具有test_child的代码继承自test_parent，该代码已实现了共享功能。我的计划是让许多类从类似parent_class的类继承，但要定义一个唯一的字段枚举和相应的映射映射。

In the following code I have test_child inherit from test_parent, which has the shared functions already implemented. My plan would be to have many classes inherit from a class like parent_class, but to define a unique 'field' enum and corresponding 'mapping' map.

#include <iostream>
#include <string>
#include <unordered_map>

class test_parent {
public:
    enum class field {
        A,
        B,
        C
    };

    typedef struct {
        std::string s;
        int i, j;
    } data_t;

    std::unordered_map<field, data_t> mapping {
        {field::A, {"A", 1, 1}},
        {field::B, {"B", 2, 2}},
        {field::C, {"C", 3, 3}}
    };

    int get_i (field f) {
        return mapping[f].i;
    }

    std::string get_s (field f) {
        return mapping[f].s;
    }   
};

class test_child : test_parent {
public:
    enum class field {
        D,
        E
    };

    std::unordered_map<field, data_t> mapping {
        {field::D, {"D", 4, 4}},
        {field::E, {"E", 5, 5}}
    };
};

int main () {
    test_parent tp;
    test_child tc;

    std::cout << tp.get_i(test_parent::field::A) << " " << tc.get_i(test_child::field::E) << std::endl;

    return 0;
}

此代码返回编译错误：

test.cpp: In function ‘int main()’:
test.cpp:55:86: error: no matching function for call to ‘test_child::get_i(test_child::field)’
std::cout << tp.get_i(test_parent::field::A) << " " << tc.get_i(test_child::field::E) << std::endl;
                                                                                    ^
test.cpp:28:6: note: candidate: int test_parent::get_i(test_parent::field)
int get_i (field f) {
    ^~~~~
test.cpp:28:6: note:   no known conversion for argument 1 from ‘test_child::field’ to ‘test_parent::field’

但是我希望打印的是：

1 5

推荐答案

不确定是不是您想要的，但是带有模板，您可以这样做

Not sure it is what you want, but with template, you might do

struct data_t
{
    std::string s;
    int i;
    int j;
};

template <typename E>
class test_parent {
public:
    int get_i(E e) const { return mapping.at(e).i; }
    const std::string& get_s(E e) const { return mapping.at(e).s; }

    static const std::unordered_map<E, data_t> mapping;
};

然后

enum class field_ABC{ A, B, C };
enum class field_DE{ D, E };

template <>
const std::unordered_map<field_ABC , data_t> test_parent<field_ABC >::mapping =  {
    {field_ABC::A, {"A", 1, 1}},
    {field_ABC::B, {"B", 2, 2}},
    {field_ABC::C, {"C", 3, 3}}
};

template <>
const std::unordered_map<field_DE, data_t> test_parent<field_DE>::mapping =  {
    {field_DE::D, {"D", 4, 4}},
    {field_DE::E, {"E", 5, 5}}
};

演示

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