enum.hpp

enum class my_big_enum
{
  /* imagine this changes a lot */
};

stores_enum.cpp

#include "stores_enum.hpp"
// we actually need the fields here.
#include "enum.hpp"

void stores_enum::method_that_uses_enum()
{
  m_e = my_big_enum::value; 
}

stores_enum.hpp

// no need to include enum.hpp, we don't use it here
// We can just re-declare it.
enum class my_big_enum;

struct stores_enum
{
  void method_that_uses_enum();
  
   my_big_enum m_e;
};