C ++ 17枚舉類型聲明

Question

我有以下枚舉typedef，並希望定義一個可以保存不同狀態的變量。

typedef enum _EventType
{
    Event1 = 0x001, Event2 = 0x002, Event2 = 0x0004
}EventType;

這就是我想要的：

EventType type = EventType::Event1 | EventType::Event2;

要么

EventType type = EventType::Event1;
type |= EventType::Event2;

V2017給我以下錯誤：

 Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast)

我知道我可以寫：

   EventType type = static_cast<EventType>(EventType::Event1 | EventType::Event2);

但代碼並不那么容易理解。

Answer 1

可以使bitor運算符重載，以便執行必要的轉換：

#include <type_traits>
#include <cstdint>

// specifying underlaying type here ensures that enum can hold values of that range
enum class EventType: ::std::uint32_t
{
    Event1 = 0x001, Event2 = 0x002, Event3 = 0x0004
};

EventType operator bitor(EventType const left, EventType const right) noexcept
{
    return static_cast<EventType>
    (
        ::std::underlying_type_t<EventType>(left)
        bitor
        ::std::underlying_type_t<EventType>(right)
    );
}

auto combined{EventType::Event1 bitor EventType::Event2};

int main()
{
}

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