Initializing union from two enumerations?

Question

C++ / C#

struct AggregationTypeAndMetalNonMetalTransitionData {
    PrimaryElementGroupType primarygrouptype; // Тип группы элемента.
    union {
        SecondaryElementGroupMetalType _metal; // Подгруппы металлов.
        NonMetalSecondaryGroupType _nonmetal; // Подгруппы неметаллов.
    } secondarytype;
    StateOfAggregationType stateofaggregation; // Агрегатное состояние вещества.
};

{PrimaryElementGroupType::nonmetals, NonMetalSecondaryGroupType::nonmetal, StateOfAggregationType::Gas}

The second initialization option does not work. Mistake

Answer 1

The second initialization option does not work

Well, yes, it doesn't work. Thus, only the first element of the union can be initialized. There is also such an initialization option, starting with C ++ 20.