Can't OR 2 enum values of the same type outside its enum class declaration - enums

Question

I am a newbie to both C++ and game programming. I am dealing with something I don't know how to make it work. I am coding along a game from a book, the authors didn't use enum class for his type but as recommended by most people, I am using enum class to remake it. It produces no error when I OR 2 enum value inside its enum class scope like this:
// This is inside the "Category.h" header file
namespace Category
{
enum class Type
{
None = 0,
SceneAirLayer = 1 << 0,
PlayerAircraft = 1 << 1,
AlliedAircraft = 1 << 2,
EnemyAircraft = 1 << 3,
Pickup = 1 << 4,
AlliedProjectile = 1 << 5,
EnemyProjectile = 1 << 6,
Aircraft = PlayerAircraft | AlliedAircraft | EnemyAircraft,
Projectile = AlliedProjectile | EnemyProjectile
};
}
But when I try to OR them inside a function of another source file, the compiler produces an error,
that is: "no operator "|" matches these operands operand type are Category::Type | Category::Type"
and here is the code inside that function (the game works for the authors version enum without class)
void World::destroyEntitiesOutsideView()
{
// This "command.category" just returns an "unsigned int" value
Command command;
// The error appears here
command.category = static_cast<unsigned int>(Category::Type::Projectile | Category::Type::EnemyAircraft);
// This is I just try to OR them alone but still the same error
Category::Type::Aircraft | Category::Type::AlliedProjectile;
}
Please someone tell me why and how can I fix this error??? Thank you a lot!!!

Answer 1

It is because you are using enum class instead of just enum. "Class enum doesn’t allow implicit conversion to int, and also doesn’t compare enumerators from different enumerations"