Re: [Boost-users] [multiindex] [bind] Update members of the container between two iterators (was: Conversion loses qualifiers)

From: Nebojsa Simic (nelle_at_[hidden])
Date: 2007-11-16 18:03:42

Nebojsa Simic wrote:
> Nebojsa Simic wrote:
>> Hello all,
>>
>> First of all, thanks for a wonderful library, it is a pleasure to work
>> with...
>>
>> However I ran into some problems and I can not find the answers either
>> on the Internet nor on this mailing list. The problem at hand concerns
>> the multiindex container and bind.
>>
>> I have a class with the following member:
>>
>> class Statistics {
>> public:
>> 	void addStats ( double val, int tick );
>> }
>>
>> and a container:
>>
>> typedef multi_index_container< Statistics,
>>     indexed_by <ordered_unique<identity<Statistics> >,
>>       ordered_non_unique< member<Statistics,double,&Statistics::gamma> >
>>     >
>>   > StatisticsMap;
>>
>> StatisticsMap m_statistic;
>>
>> indexed by :
>>
>> typedef StatisticsMap::nth_index<1>::type StatisticsByResponse;
>>
>> somewhere in code i try to do this :
>>
>> std::pair<StatisticsMap::iterator,bool> result = m_statistic.insert(
>> Statistics( response, value, tick ) );
>>
>> StatisticsByResponse& idxResponse = m_statistic.get<1>();
>> StatisticsByResponse::iterator it = m_statistic.project<1>(result.first );
>>
>> the problem comes when I try to update the statistics by using :
>>
>> for_each( it
>>     , idxResponse.end()
>>     , boost::bind( &Statistics::addStats, ::_1, val, tick )
>>   );
>>
> 
> Ok, the elements in the container are constant and may not be changed
> through iterators. For multiindex container the modify method must be
> used to change them.
> 
> So I changed the last line to :
> 
> boost::function<void(Statistics&)> fnAddStats  = boost::bind(
> &Statistics::addStats, ::_1, val, tick );
> 
> for_each( it
>     , idxResponse.end()
>     , boost::bind( &StatisticsByResponse::modify,
> boost::ref(idxResponse), ::_1, fnAddStats )
>   );
> 
> but it still does not compile (problem with boost::bind "wrong number of
> arguments").
> 
> the call :
> idxResponse.modify( it, fnAddStats );
> works, so the problem is not the first bind, but the one in for_each.
> 

this compiles:

boost::function<void(Statistics)> fnAddStats  = boost::bind(
&Statistics::addStats, ::_1, val, tick );

for_each( it
     , idxResponse.end()
     , fnAddStats
   );

but I do not think it works since the value is passed to the fnAddStats
and not the reference.

Any suggestions on how to update the members of the multiindex container
between two iterators ?

-- 
Nebojsa Simic