Restrict argument to specific class and derived class in C++

Question

I'm working on a project converting some code from a simulation language called MODSIM to C++ and have come across something I'm struggling to understand.

An example of the code is:

PlaneQueueObj = OBJECT(QueueObj[ANYOBJ:PlaneObj])

What this means is that we are declaring a class PlaneQueueObj which is inheriting from QueueObj, which only allows objects of class PlaneObj or classes derived from PlaneObj into the queue. (Classes are called objects in this language...)

I want to know how this can be implemented in C++.
It could be really obvious and I've just got myself confused but I'm new here so go easy.

Answer 1

I think what you are looking for is simply, std::queue<std::unqiue_ptr<PlaneObj>>.

i.e.

std::queue<std::unique_ptr<PlaneObj>> queue;

queue.push(new PlaneObjType1());
queue.push(new PlaneObjType2());
queue.push(new PlaneObjType3());

Answer 2

Would something like this do it?

I suppose that your queue is doing something special so that you need to implement one by yourself.

DISCLAIMER: I never wrote templates so I could be completely wrong;)

#include <vector>
#include <iostream>

template<typename T>
class QueueObj 
{
private:
    std::vector<T> queue;
public:
    void Enqueue(const T &t)
    {
        queue.push_back(t);
    }

    T Dequeue()
    {
        T t = queue.back();
        queue.pop_back();

        return t;
    }
};

class PlaneObj
{
public:
    virtual void Print()
    {
        std::cout<<"PlaneObj"<<std::endl;
    }
};

class PlaneObjDerived : public PlaneObj 
{
public:
    virtual void Print()
    {
        std::cout<<"PlaneObjDerived"<<std::endl;
    }
};

class PlaneQueueObj : public QueueObj<PlaneObj*> {};

int main()
{
    PlaneQueueObj queue;
    PlaneObjDerived *po1 = new PlaneObjDerived;
    PlaneObjDerived *po2 = new PlaneObjDerived;

    queue.Enqueue(po1);
    queue.Enqueue(po2);
    // queue.Enqueue(10); // ERROR: error C2664: 'QueueObj<T>::Enqueue' : cannot convert parameter 1 from 'int' to 'const PlaneObj &'

    po1 = static_cast<PlaneObjDerived *>(queue.Dequeue());
    po2 = static_cast<PlaneObjDerived *>(queue.Dequeue());
    po1->Print();
    po2->Print();

    return 0;
}