Vector3D in Geometry3D

class IVector3D {
public:
    double getX() = 0;
    double getY() = 0;
    double getZ() = 0;
    double getLen() = 0;
    double isCollinear() = 0;
    double getAngleCos() = 0;
}

// =>>>>>>>>>> Other file, other class CFixedVector3D

class CVector3D : public IVector3D {
    // ........
}


// =>>>>>>>>>> Other file, other class


// The idea: if points're changed, vector changes too
class CLinkedVector3D : public IVector3D {
private:
    // References here!
    CPoint3D &point_begin;
    CPoint3D &point_end;

public:
    CVector3DPointsLinked() = default;

    CVector3DPointsLinked(CPoint3D& point_begin, CPoint3D& point_end) {
        this->point_begin = point_begin;
        this->point_end = point_end;
    }

    // Other constructors
    // ...


    double getX() {
        return point_end.getX() - point_begin.getX();
    }

    // Other methods equal to CVector3D
    // ...
}