将枚举值映射到 C++ 中的类型 [英] Map enum value to a type in C++

问题描述

有没有办法将枚举值映射到 C++ 中的类型，包括 C++11.
我有以下枚举类型:

Is there any way to map enum values to types in C++, including C++11.
I have the following enum type:

enum ATTRIBUTE{AGE=0, MENOPAUSE, TUMOR_SIZE, INV_NODES, NODE_CAPS,
               DEG_MALIG, BREAST, BREAST_QUAD, IRRADIAT, CLASS};

我想将此枚举的每个值映射到特定类型.我想将 AGE 映射到 int，MENOPAUSE 映射到另一个枚举类型，BREAST 映射到 bool 等等.
那么是否有可能创建一个函数来返回一个取决于 attr 变量值的类型值?

I want to map each value of this enum to a certain type. I want to map AGE to int, MENOPAUSE to another enum type, BREAST to bool and so on.
So is it possible to create a function which returns a value of type which depends on the value of the attr variable?

//Like that:
auto value = map_attr(ATTRIBUTE attr);
//Here the type of the value variable should be int if the attr variable is AGE, bool for BREAST and so on.

推荐答案

一种惯用的方式是使用特性:

An idiomatic way to do it is using traits:

enum ATTRIBUTE{ AGE=0, MENOPAUSE, TUMOR_SIZE, INV_NODES, NODE_CAPS, DEG_MALIG, BREAST, BREAST_QUAD, IRRADIAT, CLASS };

template<ATTRIBUTE> struct Map;

template<> struct Map<AGE> {
    using type = int;
    static constexpr type value = 42;
};

template<> struct Map<MENOPAUSE> {
    using type = AnotherEnumType;
    static constexpr type value = AnotherEnumType::AnotherEnumValue;
};

// ...

然后你可以定义map_attr作为一个函数模板:

Then you can define map_attr as a function template:

template<ATTRIBUTE A>
typename Map<A>::type map_attr() { return Map<A>::value; }

并将其用作:

auto something = map_attr<AGE>();

<小时>

它遵循一个最小的工作示例:

---

It follows a minimal, working example:

#include<type_traits>

enum ATTRIBUTE{ AGE=0, MENOPAUSE };

template<ATTRIBUTE> struct Map;

template<> struct Map<AGE> {
    using type = int;
    static constexpr type value = 42;
};

template<> struct Map<MENOPAUSE> {
    using type = double;
    static constexpr type value = 0.;
};

template<ATTRIBUTE A>
typename Map<A>::type map_attr() { return Map<A>::value; }

int main() {
    static_assert(std::is_same<decltype(map_attr<AGE>()), int>::value, "!");
    static_assert(std::is_same<decltype(map_attr<MENOPAUSE>()), double>::value, "!");
}

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