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

Subject: Re: [Boost-users] Using OvenToBoost 'taken'.
From: Akira Takahashi (faithandbrave_at_[hidden])
Date: 2013-01-07 06:56:43

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

Thanks,
Akira