David Abrahams ha escrito:
on Sun Dec 09 2007, Ion Gaztañaga <igaztanaga-AT-gmail.com> wrote:
23.1.3.1 Exception safety guarantees [unord.req.except]
1 For unordered associative containers, no clear() function throws an exception. No erase() function throws an exception unless that exception is thrown by the containerâs Hash or Pred object (if any).
Why this difference? I hope someone knows the answer ;-)
Because unordered associative containers may rehash when erasing.
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). The rationale IMHO behind allowing erase to let Hash or Pred throw is to allow implementers to write iterators without bucket tracking --the bucket is computed on the fly when needed, for instance when erasing. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo