运算符重载的可变参数模板解包

Question

I have an enum, as given below. I want to have operator overloading for this enum,.

typedef enum E
{
    A = 1 << 0,
    B = 1 << 1,
    C = 1 << 2,
    D = 1 << 3,
    ANY = A | B | C | D,
}
E;

//Basic version

inline E operator |(E a, E b)
{
    return static_cast<E>(static_cast<int>(a) | static_cast<int>(b));
}

//Templated version
    template<typename T, typename Types>
    inline T operator |(T var1, Types var2) {
        return static_cast<T>(static_cast<unsigned int>(var1) | static_cast<unsigned int>(var2));
    }

    template<typename T, typename... Types>
    inline T operator |(T var1, Types... var2) {
        return static_cast<T>(static_cast<unsigned int>(var2...) | static_cast<unsigned int>(var1));
    }

I am getting following errors

error: expected ')'
        return static_cast<T>(static_cast<unsigned int>(var2...) | static_cast<unsigned int>(var1));

How do I correct it.

Thanks,

TechTotie.

Answer 1

You can try with

template<typename T, typename... Ts>
inline T operator | (T var1, Ts... var2)
{
    return static_cast<T>(  (static_cast<int>(var2) | ...) |  static_cast<int>(var1));
}

But

inline E operator |(E a, E b)
{
    return static_cast<E>(static_cast<int>(a) | static_cast<int>(b));
}

also can solve your problem