自定义类型hash

struct LogEventKey
{
    LogEventId nId = 0;   // 事件Id
    LogEventTag nTag = 0; // 事件Tag

    bool operator==(const LogEventKey& rhs) const {
        return nId == rhs.nId && nTag == rhs.nTag;
    }
    bool operator<(const LogEventKey& rhs) const {
        return nId < rhs.nId || (nId == rhs.nId && nTag < rhs.nTag);
    }
    bool operator<=(const LogEventKey& rhs) const {
        return (*this == rhs) || (*this < rhs);
    }
    bool operator>(const LogEventKey& rhs) const {
        return !(*this <= rhs);
    }
    bool operator>=(const LogEventKey& rhs) const {
        return !(*this < rhs);
    }
    bool operator!=(const LogEventKey& rhs) const {
        return !(*this == rhs);
    }
    
};//struct LogEventKey


namespace std {

    template<>
    struct hash<LogEventKey>
    {
        std::size_t operator()(const LogEventKey& key) const {
            using std::size_t;
            using std::hash;
            using std::string;

            // Compute individual hash values for first,
            // second and third and combine them using XOR
            // and bit shifting:

            return ((hash<LogEventId>()(key.nId)
                   ^ (hash<LogEventTag>()(key.nTag) << 1)) >> 1);
        }
    };

}