From: David Abrahams (dave_at_[hidden])
Date: 2007-12-11 11:05:26
on Sun Dec 09 2007, Ion GaztaÃ±aga <igaztanaga-AT-gmail.com> wrote:
> Thorsten Ottosen wrote:
>> Well, the table at
>> says that erase() does not throw for ordered containers (which is
>> correct). Anyway, this means any argument used to assume that predicate
>> evaluation is a no-throw should be the same for unordered containers.
> You are right. The draft says in 23.1 (Container requirements):
> 10 Unless otherwise specified (see 220.127.116.11 and 18.104.22.168) all
> container types defined in this clause meet the following additional
> â no erase(), pop_back() or pop_front() function throws an exception.
So it is "otherwise specified" for vector and deque.
> so the predicate for associative container should not throw, because
> erase(const key_type &k) can't throw.
> On the other hand, this seems strange. I understand making
> erase(iterator) no-throw, but I find strange making erase(const
> key_type &)don't think the standard wanted to forbid exceptions from
> the predicate. Clearly unordered containers are different:
> 22.214.171.124 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.
-- Dave Abrahams Boost Consulting http://www.boost-consulting.com
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