c++11 - C++ Forward declaring class scoped enumeration

Question

I'm wondering if it's possible to forward declare an enum that's defined within another class scope. For example, consider the following:

//A.h
class A
{
public:
    enum class type: unsigned long { /*some stuff*/ }
};

Now, in another header I'd like to forward declare the 'type' enum (suppose class B below has a function that does something with A::type)

//B.h
enum A::type; //use of undefined type 'A'

class B
{
public:
    UseTypeEnum(A::Type&);
};

This doesn't work either:

//B.h
class A;
enum A::type; //still use of undefined type

class B...

There's no problem if the enum is declared at global scope in A.h.

Is there any way to do this?

Answer 1

You can't declare nested types outside the class definition.

If you need to use them outside the class, you will have to either include the class definition, or move them into a namespace.