Forward declare typedef within C++ class

Question

What\'s the best solution to forward declare a typedef within a class. Here\'s an example of what I need to solve:

class A;
class B;

class A
{
    typedef boos         


        

Answer 1

You're facing two distinct difficulties: 1. There are no forward declarations of typedefs 2. Forward declarations of nested types are not possible

There is no way around the second: you have to unnest the types.

One way around the first that I occasionally use is to make a derived type, and that yes, can be forwardly declared.

Say:

struct Ptr : shared_ptr {};

This is a new type, but it is almost the same as a synonym. The problem, of course, is constructors, but that is getting better with C++11.

This answer, of course, is in general. For your specific case, I think you should define the Ptrs outside the classes and you would have no problem at all.

struct A;
struct B;
typedef shared_ptr APtr;
typedef shared_ptr BPtr;

and then the classes.