C ++重载| （按位或）运算符，返回常数

Question

I would like to use operator '|' in a following manner:

    switch(color){
        case Color::Red | Color::Green:
        ...

The problem is that the operator must return constant value, but I cannot make it work. I tried something like this:

    template<class T> inline const T operator| (T a, T b){ return const (T)((int)a | (int)b); }

but it doesn't do the job.

Answer 1

case should use constant expression, ie compile-time constant. Mark your operator as constexpr :

template<class T> inline constexpr T operator| (T a, T b){ return (T)((int)a | (int)b); }