Double inheritance of enable_shared_from_this

Question

I have an object (Z) which derives from two other objects (A and B).

A and B both derive from enable_shared_from_this<>, respectively enable

Answer 1

Yes, as per bad weak pointer when base and derived class both inherit from boost::enable_shared_from_this the solution is to use virtual inheritance. Here's an implementation for the C++11 standard shared_ptr (not Boost):

#include 

struct virtual_enable_shared_from_this_base:
   std::enable_shared_from_this {
   virtual ~virtual_enable_shared_from_this_base() {}
};
template
struct virtual_enable_shared_from_this:
virtual virtual_enable_shared_from_this_base {
   std::shared_ptr shared_from_this() {
      return std::dynamic_pointer_cast(
         virtual_enable_shared_from_this_base::shared_from_this());
   }
};

struct A: virtual_enable_shared_from_this {};
struct B: virtual_enable_shared_from_this {};
struct Z: A, B { };
int main() {
   std::shared_ptr z = std::make_shared();
   std::shared_ptr b = z->B::shared_from_this();
}

This isn't part of the default implementation, probably because of the overhead of virtual inheritance.