distinct_ptr.cpp

#include <iostream>
using namespace std;

// {{{
constexpr int get_hash(int hash, const char* p)
{
    return *p == '\0' ? hash : get_hash(*p * 137, p + 1);
}

template <typename T, int N>
class DistinctPtr
{
    T* p;
public:
    explicit DistinctPtr(T* p)
        : p(p)
    {}
    operator T*() const
    {
        return p;
    }
};

#define PTR(x) (DistinctPtr<decltype(x), get_hash(0, #x)>(&x))
// }}}

template <int N, int M>
void f(DistinctPtr<int, N> x, DistinctPtr<int, M> y)
{
    static_assert(N != M, "x and y are required to be distinct");
    *x = 41;
    *y = 0;
    if (*x == 41 && *y == 0)
    {
        cout << "OK" << endl;
    }
    else
    {
        cout << "FAILED" << endl;
    }
}

int main(void)
{
    int x, y;
    f(PTR(x), PTR(x));
}