How to set static member variable of template class

Question

I have a template class with a static member, but I am not sure how to set the static member variable outside of the class at runtime. Here is an example:

header.h

#ifndef HEADER_H
#define HEADER_H

template <typename T>
struct A {
  static int x;
};

template <typename T>
int A<T>::x = 7;

#endif

main.cpp

#include "header.h"

int main(int argc, char **argv) {
  // A<>::x = 8; // Want something like this to work for all template types
}

The only thing I got to work is to set it for all possible template types, e.g:

A<int>::x = 8;
A<uint8_t>::x = 8;
A<float>::x = 8;
...

but the issue is that in my code, the list of all possible types for T is very long. Is there a better solution? I could obviously just make the member not static and set it from a constructor, but the uses of the struct in my code is very deeply buried and it would not be ideal to do it that way.

Answer 1

If you have data that doesn't depend on the template parameters, I suggest that you add a non-template base that has those members:

#ifdef AHEADER
#define AHEADER
struct ABase
{
  static int x;
};
template<typename T>
struct A : ABase
{
   ...
};
#endif
#include <aheader.hpp>
int ABase::x = 8;
...
void some_func()
{
  ABase::x = 10;
}

This will not work, however, if the variable ever needs to track different values for different template types.