Compile-time constant id

Question

Given the following:

template
class A
{
public:
    static const unsigned int ID = ?;
};

I want ID to generate a unique c

Answer 1

I encountered this exact problem recently. My solution:

counter.hpp

class counter
{
    static int i;
    static nexti()
    {
        return i++;
    }
};

Counter.cpp:

int counter::i = 0;

templateclass.hpp

#include "counter.hpp"

    template 
    tclass
    {
        static const int id;
    };

    template 
    int tclass::id = counter::nexti();

It appers to work properly in MSVC and GCC, with the one exception that you can't use it in a switch statement.

For various reasons I actually went further, and defined a preprocessor macro that creates a new class from a given name parameter with a static ID (as above) that derives from a common base.