Destructors when using shared_ptr assignments

assignment.cc

#include <iostream>
#include <memory>

class Base
{
public:
    Base() { std::cout << "Base constructor" << std::endl; }
    virtual ~Base() { std::cout << "Base destructor" << std::endl; }
};

class DerivedA : public Base
{
public:
    DerivedA() { std::cout << "A constructor" << std::endl; }
    virtual ~DerivedA() { std::cout << "A destructor" << std::endl; }
};

class DerivedB : public Base
{
public:
    DerivedB() { std::cout << "B constructor" << std::endl; }
    virtual ~DerivedB() { std::cout << "B destructor" << std::endl; }
};

int main()
{
    std::shared_ptr< Base > ptr( new DerivedA );

    std::cout << "Assignment: " << std::endl;
    ptr.reset( new DerivedB );
    std::cout << "Done." << std::endl;    
    
    return 0;
}