on Thu Oct 23 2008, Chris Newbold <Chris.Newbold-AT-mathworks.com> wrote:
In trying to clean up some code in Boost.Pool, I've run afoul of some code in Microsoft's implementation of the STL where they are using allocator::rebind on an incomplete type. Something like this:
struct Node; // Incomplete!
template<typename T, typename Alloc> struct List { Alloc<T>::rebind<Node>::other::pointer node_p; ... }
I believe that attempting to instantiate an allocator with an incomplete type is illegal
Attempting to instantiate any library-defined template on an incomplete type (I think shared_ptr is the one exception to this rule now) induces undefined behavior. Thus, std::allocator<T>::rebind<X> on an incomplete X induces undefined behavior when a user does it. The library might know enough about std::allocator to do it anyway, though. It doesn't mean that instantiating any old template whose instances model Allocator on an incomplete type is illegal, though.
so, by extension, I would have assumed that attempting to rebind on an incomplete type would also be illegal, no?
I don't think that's strictly illegal -- at least not by the rule you are alluding to. It depends on what the Allocator requirements say. -- Dave Abrahams BoostPro Computing http://www.boostpro.com