In-Reply-To: <ck6la2$kki$1@sea.gmane.org> nesotto@cs.auc.dk (Thorsten Ottosen) wrote (abridged):

Conclusion: disallowing 0 will not only lead to simpler, safer programs, but it will probably also boost performance.

The null object pattern can only be used if all the object's member functions have trivial post-conditions. If instead I have code like: dog.walk_to( pTree ); assert( dog.location() == pTree ); // ... more code assuming the dog's location. then it is not going to work with a null_dog. If people use it anyway there will be tears before bedtime. Of course, this is no more an argument against ptr_vector<Dog> than it is against std::vector<Dog>. I think the problem here is the name. "ptr_vector" sounds so much like a vector of pointers that people expect null pointers to be supported. There is a gap between what those people want and what ptr_vector supplies. The null object pattern is not a solution here. It just papers over the crack. -- Dave Harris, Nottingham, UK