David M. Jones wrote:
I ran into a situation (see my "smart list" post on the boost users group) where I wanted to create a custom allocator whose pointer typedef is boost::shared_ptr. In other words, the code would look something like:
template <typename T> class my_allocator { public: typedef boost::shared_ptr<T> pointer; };
The problem with doing this is that boost::shared_ptr<T> does not have the same "interface" as the equalivalent raw pointer type T*. (I use the term interface in the generic programming/template sense; not in the object oriented sense.) One example is that there is no operator= on boost::shared_ptr that takes a raw pointer; instead reset() must be used.
Raw pointers don't necessarily have an operator= that takes another kind of raw pointer. For example, T __near * cannot be assigned T*, only itself. Similarly, shared_ptr<T> cannot be assigned T*, only itself. If a component tries to assign a T* to allocator<T>::pointer, it is broken WRT nonstandard pointers.