Joe Gottman wrote: > I just realized that it would be impossible to use weak_ptr with > any > hash. The problem is that the hash function would have to use > weak_ptr's get() method. Then if the underlying object of the > weak_ptr gets destroyed, get() will suddenly return 0 instead of the > previous pointer, so the hash function will now map the weak_ptr to a > new bucket. Is there any way to > add a member function that returns a const void * that will be > invariant > even if the underlying object of the weak_ptr has been destroyed?
weak_ptr no longer has get(). You are right that currently shared_ptr and weak_ptr work as std::map keys but not as hash_map keys, and that we need to add _some kind_ of hash table support. One easy approach is to supply a "size_t hash_value() const" member function; this will allow "expert" users to use shared_ptr/weak_ptr in a hash table by creating an appropriate hash function object _and_ equivalence object (important since shared_ptr/weak_ptr equivalence isn't a == b but !(a < b) && !(b < a)). I would rather prefer to make hash_set and hash_map work "out of the box" with a shared_ptr and weak_ptr. Unfortunately, there is no standard hash_* interface yet, and the formal proposal by Matt Austern doesn't address the problem well. _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
