----- Mensaje original ----- De: Daniel James <daniel_james@fmail.co.uk> Fecha: Martes, Diciembre 11, 2007 8:01 pm Asunto: Re: [boost] [review] Review of Unordered library begins today December7 Para: boost@lists.boost.org
Joaquín Mª López Muñoz wrote:
I think unordered containers are *not* allowed to rehash when erasing:> see N2461, 23.1.3/8
"...Rehashing invalidates iterators, changes ordering between elements,..."> and 23.1.3/12
"...The erase members shall invalidate only iterators and references> to the erased elements."
so the conclusion is that erase can't rehash (incidentally, the implications of rehashing when erasing a range would be difficult to cope with).
If a container implemented a rehash which doesn't invalidate iterators (which is certainly possible, if unlikely) then could it rehash? (Of course, such a container would have to maintain the order of the elements).
I don't think so: even if you manage to implement an iterator-conscious, order-preserving, sensible rehashing mechanism, getting new memory can throw std::bad_alloc, which is not allowed (only throwing from Hash or Pred permitted)--unless you catch such exceptions internally... but this is rather artificial. My opinion is that the writers of this piece of the C++0x standard didn't consider rehashing as a permissible operation when erasing. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo