variable_inliner

build.sh

#!/bin/bash
clang++ -c -std=c++11 -stdlib=libc++ main.cpp
clang++ -c -std=c++11 -stdlib=libc++ sub.cpp
clang++ main.o sub.o -o main

constant.hpp

#pragma once

#include "variable_inliner.hpp"

namespace test_ns {
    struct custom {
        int x;
    };

    namespace {
        custom &c = bbb::variable_inliner<custom>::get();
    };
};

main.cpp

#include <iostream>
#include "constant.hpp"
#include "sub.hpp"

int main(int argc, char *argv[]) {
    std::cout << "main 1: " << test_ns::c.x << std::endl;
    test_ns::c.x = 1;
    std::cout << "main 2: " << test_ns::c.x << std::endl;

    sub_func();
    
    std::cout << "main after sub: " << test_ns::c.x << std::endl;
}

sub.cpp

#include <iostream>
#include "constant.hpp"

#include "sub.hpp"

void sub_func() {
    std::cout << "sub 1: " << test_ns::c.x << std::endl;
    test_ns::c.x = 2;
    std::cout << "sub 2: " << test_ns::c.x << std::endl;
}

sub.hpp

#pragma once

void sub_func();

variable_inliner.hpp

#pragma once

namespace bbb {
    template <typename variable_type, typename tag = variable_type>
    struct variable_inliner {
        static variable_type &get() {
            static variable_type _;
            return _;
        };
    };
};