Question

dI am programming a simulation. Now it should both work with 2D and 3D, so I’m trying to make my classes work with 2D- and 3D-Vectors. Also the Vectors should have an template parameter to indicate which type should be used for the coordinates.

My base class looks like this:

class SimulationObject {
    AbstractVector<int>* position;
    AbstractVector<float>* direction;
}

Now the problem is, I can’t use polymorphism, since then all my Vectors would have to be pointers and this makes operator-overloading nearly impossible for operations like this:

AbstractVector<float>* difference = A.position - (B.position + B.direction) + A.direction;

But also I can’t use a template parameter to specify which type to use:

template <typename T> class Vector2d;
template <typename T> class Vector3d;

template <class VectorType> class SimulationObject {
    VectorType<int> position;
    VectorType<float> direction;
}


SimulationObject<Vector2D> bla; 
//fails, expects SimulationObject< Vector2D<int> > for example.
//But I don't want to allow to specify
//the numbertype from outside of the SimulationObject class

So, what do?

Answer 1

You can use template template parameters:

template <template <class> class VectorType> 
class SimulationObject {
    VectorType<int> position;
    VectorType<float> direction;
};