using namespace boost;
class A {};
class B : public A {};
class X {
virtual shared_ptr<A> foo();
};
class Y : public X {
virtual shared_ptr<B> foo();
};
The return types aren't covariant (nor are they, therefore, legal), but they would be if I was using raw pointers instead. What's the commonly accepted idiom to work around this, if there is one?
I think that a solution is fundamentally impossible because covariance depends on pointer arithmetic which is incompatible with smart pointers.
When Y::foo
returns shared_ptr<B>
to a dynamic caller, it must be cast to shared_ptr<A>
before use. In your case, a B*
can (probably) simply be reinterpreted as an A*
, but for multiple inheritance, you would need some magic to tell C++ about static_cast<A*>(shared_ptr<B>::get())
.