C ++对类/结构内定义的公共别名（typdef / using）的循环依赖

Question

Is there a way to break circular dependencies like the following without moving both using/typedef aliases outside classes?

// header A.h
#ifdef A
#define A
#include "B.h"
class A {
  using ID = uint32_t;
  void some_func(B::ID id);
};
#endif A


// header B.h
#ifdef B
#define B
#include "A.h"
class B {
  using ID = uint64_t;
  void some_func(A::ID id);
};
#endif B


// main.cpp
#include "A.h"
int main() {...}

Assume guard #ifdef s are present and ID can be a more complex type (a struct etc.).

Edit: a bit of clarification: alias names are not necessarily the same (ie not ID ).

Modified example:

// header A.h
#ifdef A
#define A
#include "B.h"
class A {
  using SomeAliasInA = uint32_t;
  void some_func(B::SomeAliasInB id);
};
#endif A


// header B.h
#ifdef B
#define B
#include "A.h"
class B {
  using SomeAliasInB = std::string;
  void some_func(A::SomeAliasInA id);
};
#endif B

Answer 1

Create an external file for type definitions:

template<typename T>
struct types{};

class A;
class B;

template<>
struct types<A>{
    using alias = std::string;
};

template<>
struct types<B>{
    using ID = bool;
    using alias_2 = int;
    using alias_3 = short;
};

You can then use it like so:

class A{
    void foo(types<B>::ID id);
};
class B{
    void foo(types<A>::alias id);
};