on Fri Dec 07 2007, Ion Gaztañaga <igaztanaga-AT-gmail.com> wrote:
Thorsten Ottosen wrote:
I vote to accept this library. The documentation is very nice.
Thanks for the vote.
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"
Under what cicumstances can/should/would I construct a ahsh or predicate that throws? I mean, the hash computes an integer, and comparisons reads data to determine its answer.
This migth be what the standard requires, but it certainly seems non-intuitive. Why not just require that neither hash nor predicates can throw?
The same could be said about Predicate for ordered containers like std::set/map. I haven't seen a practical case where the comparison could throw. But standard library experts should answer this better than me.
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. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com