C++: using-statement of forward-declared class generates error C2371

Question

//A.h
class A;

//A.cpp
#include A.h
class MyA {};
using A = MyA; // error C2371  'A' : redefinition; different basic types

https://ideone.com/Aifxy2

A lot of legacy code uses the class name A .

I want new code to use the name MyA , without breaking existing code.

However, when I try to do so, I get the error C2371: 'A': redefinition; different basic types

Answer 1

//A.h
class MyA;
using A = MyA;

//A.cpp
#include A.h
class MyA {};