Re: [boost] [review] Review of Unordered library begins today December 7

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2007-12-10 09:40:53

Daniel James skrev:
> On 09/12/2007, Thorsten Ottosen <thorsten.ottosen_at_[hidden]> wrote:
>> Well, the table at
>>
>> http://igaztanaga.drivehq.com/unordered/unordered/comparison.html
>>
>> 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.
> 
> comp.std.c++ would be the place to discuss logical inconsistencies in
> the standard.

Right, but we are allowed to investigate potential problems if we see 
them :-)

>> Why does erase( const_iterator ) (and range version), not provide the
>> no-throw guarantee?
> 
> Because that's what the standard says... Perhaps I'm being pedantic in
> my reading, the intent might have been that the hash function is never
> called during those overloads of erase.
> 
> This implementation actually does provide the no throw guarantee. But
> Jeremy Maitin-Shepard's version (on which it is based) didn't because
> the iterators didn't store the bucket, and required the hash to be
> calculated to work out which bucket the elements to be deleted are in.
> Which I think the standard allows.

Ok, I think you right the standard allows that. But this is also
a bit irritating, because I cannot portable take advantage of your
stronger guarantee. feThis again begs the question of how much the 
stronger guarantee affects performance?

>> Does erase give the strong guarantee otherwise?
> 
> Exceptions are only allowed from the hash or predicate objects. So no
> throw if they are no throw.

yes, but my question was: *if an exception is thrown*, then what? I 
assume you give the basic guarantee?

-Thorsten