Re: standard vs. hand crafted loops

From:

Carl Barron <cbarron413@adelphia.net>

Newsgroups:

comp.lang.c++.moderated

Date:

10 May 2006 14:43:48 -0400

Message-ID:

<090520062217106840%cbarron413@adelphia.net>

In article <1147114512.131883.144670@v46g2000cwv.googlegroups.com>,
<pavel.turbin@gmail.com> wrote:

I've seen many times advise to use standard loops e.g. for_each,
instead of iterator and for loop. I was trying to follow this hint.
But, it looks it involves extra complexity and the code getting larger
without any benefits for me.

for example: count length of each string wrapped into another object
(MyData):

    I can't write anything more concise than the hand code loop using
just the standard library using std::accumulate which is more like what
you are doing it requires a binary functor,

This functor can be created inline with accumulate using either
boost::bind, or phoenix v1 below.

the binary functor can be created via boost[tr1] bind like this:

#include <iostream>
#include <ostream>
#include <boost/bind.hpp>
#include <vector>
#include <numeric>
#include <functional>

int main()
{
    std::vector<std::string> data;
    data.push_back("one");
    data.push_back("four");
    typedef std::string::size_type size_type;
    size_type total = std::accumulate
       (
          data.begin(),
          data.end(),
          size_type(0),
          boost::bind
          (
             std::plus<double>(),
             _1,
             boost::bind
             (
                &std::string::size,
                _2
             )
          )
       );
    std::cout << "7 == "<< total << '\n';
}

or using phoenix 1.x in boost spirit library but it is independent of
spirit the functor can be created as:

#include <iostream>
#include <ostream>
#include <boost/spirit/phoenix.hpp>
#include <vector>
#include <numeric>

using namespace phoenix;

int main()
{
    std::vector<std::string> data;
    data.push_back("one");
    data.push_back("four");
    typedef std::string::size_type size_type;
    size_type total = std::accumulate
       (
          data.begin(),
          data.end(),
          size_type(0),
          arg1 + bind(&std::string::size)(arg2)
       );
    std::cout << "7 == "<< total << '\n';
}
  the loop could be written as:
    total = std::accumulate(data.begin(),data.end(),size_type(0),
       arg1 + bind(&std::string::size)(arg2) );

which is almost as short and almost as readable as the hand coded loop.

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