C++11 standard conformant bitmasks using enum class

Question

Can you implement standard conformant (as described in 17.5.2.1.3 of the n3242 draft) type safe bitmasks using enum class? The way I read it, a type T is a bitmask if it support

Answer 1

I'm not entirely sure what your acceptance criteria are, but you can just make operator & return a wrapper class with appropriate conversions and an explicit operator bool:

#include 

template using Underlying = typename std::underlying_type::type;
template constexpr Underlying
underlying(T t) { return Underlying(t); }

template struct TruthValue {
    T t;
    constexpr TruthValue(T t): t(t) { }
    constexpr operator T() const { return t; }
    constexpr explicit operator bool() const { return underlying(t); }
};

enum class Color { RED = 0xff0000, GREEN = 0x00ff00, BLUE = 0x0000ff };
constexpr TruthValue
operator&(Color l, Color r) { return Color(underlying(l) & underlying(r)); }

All your other operators can continue to return Color, of course:

constexpr Color
operator|(Color l, Color r) { return Color(underlying(l) | underlying(r)); }
constexpr Color operator~(Color c) { return Color(~underlying(c)); }

int main() {
    constexpr Color YELLOW = Color::RED | Color::GREEN;
    constexpr Color WHITE = Color::RED | Color::GREEN | Color::BLUE;
    static_assert(YELLOW == (WHITE & ~Color::BLUE), "color subtraction");
    return (YELLOW & Color::BLUE) ? 1 : 0;
}