c++ - How can I use an enum class in a boolean context?

Question

I have some generic code that works with flags specified using C++11 enum class types. At one step, I'd like to know if any of the bits in the flag are set. Currently, I'm using the code:

if (flags != static_cast<E>(0)) // Works, but ugly.

I could also force users to specify a particular name for an all-zero field, which is more readable but imposes my naming conventions on anyone using it:

if (flags != E::none) // Works, if you manually define none = 0.

But neither of these reads as nicely as the traditional:

if (flags) // Doesn't work with class enums.

Is it possible to specify a custom function to evaluate a class enum in a boolean context?

Answer 1

Like @RMatin says. But you could overload operator!

bool operator!(E e) {
  return e == static_cast<E>(0);
}

So that you can use the !!e idiom

if(!!e) {
  ...
}