Question

I am actually not really aware if you can declare a class and then use a static instance it among several objects of the same class. More specifically:

class State {
    public:
        State();
        static CustomNumberDist normal_dist;
    private:
        int id;   
};

So every instance of State should contain the same instance of CustomNumberDist. I compiles but I am wondering if it is valid or I may run into problems later on.

Answer 1

The declaration (header file i.e. .h) that you have given is perfectly valid.

However in the definition (.cpp file) you need

State::CustomNumberDist normal_dist;

As memory will be required for the static object when you get to the linking stage.