The canonical way to prevent a class from being instantiated is by making its constructor private. To actually get one of the desired instances, you call a static method, which returns a reference to a constructed object.
class Me {
public:
static Me &MakeMe() { return Me(); }
private:
Me();
}; // Me
This doesn't help of course - but it'd probably make the programmer pause!
int main() {
Me(); // Invalid
Me m; // Invalid
Me::MakeMe(); // Valid - but who'd write that?
Me m = Me::MakeMe();
} // main()
I know this isn't a direct analog to the Guard instances that you describe - but maybe you could adapt the concept?
