Check if an integral type could be safely cast to an enum.

enum_check.h

template <typename TEnumType, TEnumType... EValues>
struct EnumCheck;

template <typename TEnumType>
struct EnumCheck<TEnumType>
{
    template <typename IntegralType>
    static constexpr bool is_valid(IntegralType value)
    {
        return false;
    }
};

template <typename TEnumType, TEnumType ECurrent, TEnumType... ERest>
struct EnumCheck<TEnumType, ECurrent, ERest...>
{
    using SubCheck = EnumCheck<TEnumType, ERest...>;

    template <typename IntegralType>
    static constexpr bool is_valid(IntegralType value)
    {
        return (value == static_cast<IntegralType>(ECurrent)) || SubCheck::is_valid(value);
    }
};


enum class Color { red, green, blue };
using ColorCheck = EnumCheck<Color, Color::red, Color::green, Color::blue>;


int main()
{
    ColorCheck::is_valid(0);
    ColorCheck::is_valid(1);
    ColorCheck::is_valid(2);
    ColorCheck::is_valid(-2);
    ColorCheck::is_valid(3);
    return 0;
}