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

As others have noted, you cannot forward-declare typedefs. That's in part because typedefs aren't really "types" of their own, but aliases for other types (hence the C++11 equivalent notion of a "type alias" such as "using Int = int;"). That means, for example, that typedefs don't show up in ABI elements such as mangled names, and so the compiler really has to know enough of the underlying type to satisfy all ABI requirements (including how to mangle the type name).