enum X Macro

example.cpp

///////////////////////////////////////////////
// header

#include <string_view>

#define RAINBOW(X) \
    X(Red) \
    X(Orange) \
    X(Yellow) \
    X(Green) \
    X(Blue) \
    X(Indigo) \
    X(Violet)

enum class Rainbow {
    #define M(X) X,
    RAINBOW(M)
    #undef M
};

// returns "" on error.
std::string_view RainbowToString(Rainbow);

// returns nullptr on error.
const Rainbow* RainbowFromString(std::string_view);

///////////////////////////////////////////////
// implementation 

#include <unordered_map>

std::string_view RainbowToString(Rainbow v) {
    switch (v) {
        #define M(X) case Rainbow::X: return #X;
        RAINBOW(M)
        #undef M

    }
    return "";
}

const Rainbow* RainbowFromString(std::string_view v) {
    static const std::unordered_map<std::string_view, Rainbow> m{
        #define M(X) {#X, Rainbow::X},
        RAINBOW(M)
        #undef M
    };
    auto s = m.find(v);
    return s != m.end() ? &(s->second) : nullptr;
}