[boost] shared_ptr type_info, void cast

From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2007-05-21 14:42:22

I'd like to request the following functions added to shared_ptr's interface:

template <class T>
void * shared_ptr<T>::void_cast() const;

template <class T>
std::type_info const & shared_ptr<T>::type() const;

The first function mimics the use of dynamic_cast<void *>(p) for pointers to 
polymorphic objects. The second function is similar to typeid(r), for 
references to polymorphic objects. Of course, void_cast needs to be 
specialized to apply the correct modifiers of T to the returned pointer 
type.

There are two scenarios that need those functions:

- when using shared_ptr<T> in contexts where T is incomplete (or void);

- when the T in shared_ptr<T> has nothing to do with the type of the object 
managed by the shared_ptr's control block. For example, through the recently 
introduced aliasing constructor, it is possible for a shared_ptr<int> to 
manage the lifetime of an object of some user-defined type that has the int 
as a member.

Both functions are critical for implementing proper serialization of 
shared_ptr objects.

Emil Dotchevski