bad weak pointer when base and derived class both inherit from boost::enable_shared_from_this

Question

I have a base class which derives from boost::enable_shared_from_this, and then another class which derives from both the base class and boost::enable_shared_from_this:

Answer 1

Here's how I would solve your problem:

#include 
#include 

using namespace boost;

class virt_enable_shared_from_this :
   public enable_shared_from_this
{
 public:
   virtual ~virt_enable_shared_from_this() {}
};

template 
class my_enable_shared_from_this : virtual public virt_enable_shared_from_this
{
 public:
   shared_ptr shared_from_this() {
      return dynamic_pointer_cast(virt_enable_shared_from_this::shared_from_this());
   }
};

class A : public my_enable_shared_from_this { };

class B : public my_enable_shared_from_this { };

class C : public A, public B, public my_enable_shared_from_this {
 public:
   using my_enable_shared_from_this::shared_from_this;
};

int main() {
   shared_ptr c = shared_ptr(new C());
   shared_ptr c_ = c->shared_from_this();

   return 0;
}

This is painful and at least a bit ugly. But it works reasonably well, after a fashion. I think Fraser's idea of re-thinking your design is likely the better option.