Re: [boost] [review] Review of Unordered library begins today December7

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2007-12-12 13:24:32

Eric Niebler ha escrito:

> David Abrahams wrote:
> > on Tue Dec 11 2007, Joaquín Mª López Muñoz <joaquin-AT-tid.es> wrote:
> >
> >> 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 container’s 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
> >
> > Sorry, how do you reach that conclusion?  It says that erase can
> > invalidate iterators, and the only thing it says that rehashing
> > invalidates is iterators.
>
> If I'm understanding correctly, erase can only invalidate iterators (to
> the erased elements*, but rehashing invalidates iterators to all
> elements. Therefor, erase cannot rehash. Did I get that right?

This is exactly how I'm interpreting the standard (draft), yep.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo