How to write a custom deleter with a templateized QSharedPointer

I am trying to write a templatized wrapper to a class such that the wrapper can manage the lifespan using a shared pointer. (I can’t modify the class(es) that I’m wrapping)

I would like to write a custom deleter such that I can debug and validate that the objects are being release at the correct time.

#include <QtCore/QCoreApplication>
#include <QSharedPointer>

class A {
public:
    virtual ~A() {
        qInfo() << "Deleting an A";
}
    void doA(void) {
        qInfo() << "Doing A thing";
    }

};

class B : public A {

};

class SharedA {
public:
    QSharedPointer<A> m_spA;
};

//
//template<class T> void DeleteB(T* p) {
//    qInfo() << "deleting shared";
//    delete p;
//}


template<class T>
class SharedB :public SharedA {
public:
    static void DeleteB(T* p) {
        qInfo() << "deleting shared";
        delete p;
    }
    SharedB() {
        m_pB = new B;
        A* pA = dynamic_cast<A*>(m_pB);
        m_spA = QSharedPointer<A>(pA, DeleteB);
    }
    B* m_pB;
};


void lifespan() {
    SharedB<B> bThing;
    bThing.m_pB->doA();

}

int main(int argc, char* argv[])
{
    QCoreApplication a(argc, argv);

    lifespan();

}

Unfortunately I end up with the following syntax error:

Error   C2664   'void (T *)': cannot convert argument 1 from 'T *' to 'T *' testshared  Qt\6.4.1\msvc2019_64\include\QtCore\qsharedpointer_impl.h   79  

>Solution :

If you keep managing with QSharedPointer<A>,

static void DeleteB(T* p) {
    qInfo() << "deleting shared";
    delete p;
}

should be

static void DeleteB(A* a) {
    auto p = static_cast<T*>(a);
    qInfo() << "deleting shared";
    delete p;
}