shared_ptr<Base> and objects from derived classes

Question

Given something like this:

class Base {...};
class D1 : public Base {...};
class D2 : public Base {...};

In my code, is it legal to use std::shared_ptr<Base> to manage the lifetime and pass around objects of types D1 and D2? Or could this cause a world of pain?

Answer 1

Yes it is completely fine. Smart pointers are designed to be drop-in replacements for dump pointers.

Of course you have to think about whether to make Base's member functions virtual, just like you would with dumb pointers.

Answer 2

If the following is possible to do

Base* ptr_base = new Derived()

Then the following should also be true

std::shared_ptr<Derived> ptr_derived = std::make_shared<Derived>();
std::shared_ptr<Base> ptr_base = ptr_derived;
// The shared pointer count is 2 as logically there are 2 handles to
// to the same memory object.

After this the base shared pointer can be used for run-time polymorphism as we used to use raw pointers for the same.