将枚举值映射到C++中的类型

Question

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:

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某种类型.我要地图AGE来int,MENOPAUSE另一个枚举类型,BREAST为bool等等.
那么是否可以创建一个函数来返回一个取决于attr变量值的类型值？

//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.

Answer 1

一种惯用的方法是使用特征:

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为一个功能模板:

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

并将其用作:

auto something = map_attr<AGE>();

它遵循一个最小的工作示例:

#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, "!");
}