Re: [Boost-users] Using OvenToBoost 'taken'.

Subject: Re: [Boost-users] Using OvenToBoost 'taken'.
From: Robert Jones (robertgbjones_at_[hidden])
Date: 2013-01-07 08:43:54

On Mon, Jan 7, 2013 at 11:56 AM, Akira Takahashi <faithandbrave_at_[hidden]>wrote:

> Hi Robert,
>
> 2013/1/7 Robert Jones <robertgbjones_at_[hidden]>
>
>> Hi Folks
>>
>> This question is about using the OvenToBoost port, not currently part of
>> Boost, but likely to be soon, I understand.
>>
>> The code below evaluates the predicate for the first and second elements
>> of the array. The evaluation of the
>> second element seems to me to be unnecessary and wrong, since the 'taken'
>> adaptor knows the range is
>> ended after the first element is taken.
>>
>> Thoughts?
>>
>> Thx, Rob.
>>
>> #include <boost/range/adaptor/filtered.hpp>
>> #include <boost/range/adaptor/taken.hpp>
>> #include <boost/range/algorithm/for_each.hpp>
>> #include <iostream>
>>
>> bool predicate( int i )
>> {
>>     std::cout << "predicate(" << i << ")" << std::endl;
>>     return true;
>> }
>>
>> void doNothing( int ) { }
>>
>> int main( )
>> {
>>     int array[ ] = { 0, 1, 2, 3, 4, 5 };
>>
>>     for_each( array | boost::adaptors::filtered( predicate ) |
>> boost::adaptors::taken( 1 ), doNothing );
>> }
>>
>>
> `filtered` adaptor (boost::filter_iterator) is over call predicate for
> skip element.
> This is boost::filter_iterator's specification. see:
> http://www.boost.org/doc/libs/1_52_0/libs/iterator/doc/filter_iterator.html
>
> So it does... ok thx for that!

- Rob.