Re: [boost] for_each abstraction

Subject: Re: [boost] for_each abstraction
From: Karsten Ahnert (karsten.ahnert_at_[hidden])
Date: 2010-11-17 14:55:22

> What do you mean by "handles"?  Do you want to just package up the
> for_each function together with the sequence type you want to operate
> on, effectively reducing everything to a unary function accepting the op
> parameter?  I don't know of such an abstraction in boost.

Yes, exactly. This looks like a quite general concept for me and I was
wondering if something has already been implemented.

Maybe a small example is:

struct std_algorithm
{
  template< Op >
  static void for_each( std::vector< double > &vec , Op op )
  {
    std::for_each( vec.begin() , vec.end() , op );
  }
};

struct thrust_algorithm
{
  template< Op >
  static void for_each( thrust::device_vector< double > &vec , Op op )
  {
    thrust::for_each( vec.begin() , vec.end() , op );
  }
};

// the complex algorithm we want to implement
template< class Algorithm , class Sequence >
void do_something( Sequence &seq )
{
  ...
  Algebra::for_each( seq , op() );
  ...
}

// use youe code via

// the standard version
std::vector< double > vec1;
do_something< std_algorithm >( vec1 );

// the thrust (CUDA) version
thrust::device_vector< double > vec2;
do_something< thrust_algorithm >( vec2 );

> There was a topic that was brought up by...I'm going to say Joel Falcou,
> but I may have that wrong...discussing segmented iterators and iteration
> in general (I would search "segmented iterators").  I believe his use
> case was enabling the use of simd instruction in the iteration, which
> required special treatment of the first few and last few elements of the
> range.  One abstraction that makes this efficient is to push the
> iteration to the responsibility of the range or sequence you're
> operating on.  This seems to be roughly what you might want to consider
> doing here (and is basically equivalent to packaging the for_each
> function up with the sequence, as I suggested above).

I think you mean this one

http://thread.gmane.org/gmane.comp.lib.boost.devel/209431

altough I am not sure I fully understand.

Karsten