How to - forward declare a nested class or all also within namespace, -
If there is inclusion of declared class to declared earlier in other file ? So - impossible to make a include?
Thanks.

(double side reference) ??
Like:

file1.h ----
#include "file2.h"
namespace 1_2
{

class 1
{
public:
host* member_host;
class 2{};
};

}

file2.h---

//impossible to include file1.h !!! -only forward declarations !
class host
{
class2* member; //Errors - 'class2 -undefined'
};

};#include "file2.h" #include "file2.h"