问题
Is there a way to ensure a template parameter is an enum-class type?
I know type_traits has std::is_enum, but I don't want it to match regular enums, just enum_classes.
Example of the wanted effect:
enum class EnumClass {};
enum Enum {};
class Class {};
template <typename T>
void Example()
{
static_assert(/* T is EnumClass */, "`T` must be an enum class");
}
Example<EnumClass>(); // Ok
Example<Enum>(); // Error
Example<Class>(); // Error
I am using C++11, and unfortunately cannot go any higher (though I'd be curious to know the solution anyway, even if it involves newer standards).
Is it possible?
回答1:
You can achieve it with:
template<typename T>
using is_class_enum = std::integral_constant<
bool,
std::is_enum<T>::value && !std::is_convertible<T, int>::value>;
Here a demo.
If you prefer using SFINAE, the same can be achieved with:
template<typename T, typename _ = void>
struct is_class_enum : std::false_type {
};
template<typename T>
struct is_class_enum <
T,
typename std::enable_if<std::is_enum<T>::value &&
!std::is_convertible<T, int>::value>::type> :
public std::true_type {
};
来源：https://stackoverflow.com/questions/39807629/ensure-template-parameter-is-an-enum-class