struct struct_sample
{
     ...
};

void byPtr(struct_sample *a)
{
       // 'a' point to 'base' memory location
       // 'a' and 'base' is the same object (a == base) (value of address is same)
        a->some_function();
}
void byRef(struct_sample &a)
{
       // '&a' have the same memory location of 'base'
       // 'a' and 'base' is the same object (&a == base)
       a.some_function();
}
void byCopy(struct_sample a)
{
       // 'a' is modified but not 'base' (&a != base)
       // 'a' and 'base' is not the same object
       a.some_function();
}

int main(..........
{

       struct_sample *base = new struct_sample;
       byPtr(base);
       byRef(*base);
       byCopy(*base);
}

template<typename T>
class Factory
{
       .... make your function to create enemy of type T, register to your manager, .... etc ...
};

class GenericSpawner : public Factory<{class of your base entity}>,
                       public {class of your base entity for setPosition/setRotation/serialize/...}
{
        ... make function to spaw enemy using derived function getPosition/getRotation/...
};