Reusable std::shared_ptr

Question

Is it possible to make std::shared_ptr not to delete an object, but move it to a list?

#include <memory>
#include <list>

struct QObject { double socialDistance; };

int main()
{
    std::list<QObject *> free_objects;
    std::list<QObject *> used_objects;
    
    QObject* p_object = new QObject{10};
    
    free_objects.push_back(p_object);
    
    {
        std::shared_ptr<QObject> p(p_object);
    }
    
    //At this point p_object is moved from free_objects to used_objects,
    //so I reuse the object later.

    return 0;
}

If yes, is it possible to reuse not only the objects but also the control block to avoid memory reallocation?

Answer 1

Is it possible to make std::shared_ptr not to delete an object, but move it to a list?

You might use custom deleter for that:

std::shared_ptr<QObject> p(p_object, [&](QObject* p){
                used_objects.push_back(p);
                auto it = std::find(free_objects.begin(), free_objects.end(), p);
                if (it != free_objects.end()) free_objects.erase(it);
            });

Demo