From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2007-12-11 11:45:30
David Abrahams skrev:
> on Fri Dec 07 2007, Ion GaztaÃ±aga <igaztanaga-AT-gmail.com> wrote:
>> Thorsten Ottosen wrote:
>>> One thing puzzled me though:
>>> (see http://igaztanaga.drivehq.com/unordered/unordered/comparison.html)
>>> "The containers hash or predicate function can throw exceptions from erase"
>> Certainly, Daniel has tried to achieve strong exception guarantees and
>> the implementation becomes quite complicated if comparison/hash throws.
>> Double buffering and other tricks are needed. I think this is a very
>> good question both for boosters and people from the LWG.
> When specifying requirements in the standard, we (the LWG) don't like
> to constrain implementations or users if possible. I don't see any
> reason to forbid a throwing comparison or hash.
Right, but this is often a double-edged sword. Think of problems with
allowing std::list<T>::size() to be O(n).
What is flexibility for the implementer is often a synonym for
non-portability for the user. As a library implementer I have to be
conservative w.r.t. the exceotion-safety guarantees given which means
the additional guarantees given by some implementations cannot be taken
advantage of. Of course, I might take advantage of them in non-generic
code, but then at the expense of being non-portable.
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