covariant return types and std::unique_ptr

Hi,

I was just wondering the other day what the preferred way of rewriting
the following code fragment (using covariant return types) in C++11
(using std::unique_ptr for the return types) would be:

   struct A
   {
     virtual A *createAnother() = 0;
     virtual void foo() = 0;
   };

   struct B : A
   {
     B *createAnother()
     {
       B *b = new B(*this);
       b->doSomeStuff();
       return b;
     }

     void foo();
     void bar();

   private:
     void doSomeStuff();
   };

   int main()
   {
     B *b1 = new B();

     B *b2 = b1->createAnother();
     b2->foo();
     b2->bar();
   }

Obviously, just replacing the raw pointers with std::unique_ptr won't
work (without some additional casts) - but what's the cleanest way to
make it work (with the emphasis being on "cleanest")?

Christof

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