boost::any (2) - storing pointers in boost::any

We know that we can retrieve the value stored in a boost::any using one of the two overloaded boost::any_cast by either passing our any by reference or as a pointer. What if we store a pointer in boost::any?

The following example assumes the declaration from the previous boost::any(1) post:

int main()
{
    typedef std::vector<boost::any> MixedContainer_t;
    MixedContainer_t mixedContainer;

    A* aPtr1 = new A(2);
    A* aPtr2 = new A(3);

    mixedContainer.push_back(aPtr1);
    mixedContainer.push_back(aPtr2);

    //would not work. What is stored at front() is a pointer to A
    //and not an object of type A.
    if(A* a = boost::any_cast<A> (&mixedContainer.front()))
        a->print();

    //we can even confirm it by testing the types
    if(typeid(A*) == mixedContainer.back().type())
    {
        std::cout << "object at front() is a pointer to A" << std::endl;
    }
    //to get a pointer to it, we need to retrieve a A**, and pass
    //the type of object we think stored at front as A*
    if(A** a = boost::any_cast<A*> (&mixedContainer.front()))
    {
        std::cout << "pointer-> ";
        (*a)->print();
    }
    
}

Storing pointers in boost::any is problematic, because boost::any stores only a value of the pointer, and when the boost::any is destroyed, the only memory that is released is that occupied by the pointer, and not the memory it points to. That is, delete or delete[] is not called. What to do? Use smart pointers. As with standard containers, avoid using auto_ptr because of its 'weird' copy semantics.

#include <iostream>
#include <vector>
#include <boost/any.hpp>
#include <boost/shared_ptr.hpp>


class A
{
    int value_;
public:
    A(int value) : value_(value) {}
    void print() const {std::cout << "A's value: " << value_ << std::endl;}
    ~A() {std::cout << "A(" << value_ <<") destructor" << std::endl; }
};

class B
{
    int value_;
public:
    B(int value) : value_(value) {}
    void print() const {std::cout << "B's value: " << value_ << std::endl;}
    ~B() {std::cout << "B(" << value_ <<") destructor" << std::endl; }
};

int main()
{
    typedef std::vector<boost::any> MixedContainer_t;
    MixedContainer_t mixedContainer;

    boost::shared_ptr<A> aPtr0(new A(1));
    A* aPtr1 = new A(2);
    A* aPtr2 = new A(3);

    mixedContainer.push_back(aPtr0);
    mixedContainer.push_back(aPtr1);
    mixedContainer.push_back(aPtr2);

    //and to retrieve the value from shared Ptr is simple
    try
    {
        boost::shared_ptr<A> ptr = boost::any_cast<boost::shared_ptr<A> > (mixedContainer.front());
        ptr->print();

    }
    catch(boost::bad_any_cast& bac)
    {
        bac.what();
    }
    //only the destructor of the A pointed to by shared_ptr is printed.
}