Re: [Boost-users] [Lambda] Lost in lambda land!

Subject: Re: [Boost-users] [Lambda] Lost in lambda land!
From: Michael Caisse (boost_at_[hidden])
Date: 2010-03-23 17:17:51

Robert Jones wrote:
> Hi Folks,
>
> Can anyone tell me why this is wrong? My intention is to call A::f() 
> for each A constructed
> on-the-fly from the elements of v.
>
> Thanks, Rob.
>

Hi Rob -

Since I'm promoting phoenix these days  (o;

Here is one way you could do it --------------------

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

struct A
{
      A( int i ) : i_( i ) {}
      void f(){ std::cout << i_ << std::endl; }

      int i_;
};

int main()
{
   using namespace boost::phoenix;
   using namespace boost::phoenix::arg_names;
   using namespace boost::phoenix::local_names;

   std::vector< int > vec;

   // fill the vector with something
   for( int i=0; i < 10; ++i )
   {
      vec.push_back( i );
   }

   // create an A for each vector entry
   std::for_each( vec.begin(), vec.end(),
          let( _a = construct<A>(arg1) )
          [
             bind( &A::f, _a )
                  ]
      );

   return 0;
}

------------------------------------------------

And now say we want to do something a little more interesting ... like 
store the newly constructed object in a vector also.

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

struct A
{
      A( int i ) : i_( i ) {}
      void f(){ std::cout << i_ << std::endl; }

      int i_;
};

int main()
{
   using namespace boost::phoenix;
   using namespace boost::phoenix::arg_names;
   using namespace boost::phoenix::local_names;

   std::vector< int > vec;
   std::vector< A > a_vec;

   // fill the vector with something
   for( int i=0; i < 10; ++i )
   {
      vec.push_back( i );
   }

   // create an A for each vector entry, call f()
   // on the object and store it in a vector
   std::for_each( vec.begin(), vec.end(),
                  let( _a = construct<A>(arg1) )
                  [
                     bind( &A::f, _a ),
                     push_back( ref(a_vec), _a )
                  ]
      );

   // print out our vector of A's using a phoenix bind
   // to a member variable
   std::for_each( a_vec.begin(), a_vec.end(),
                  ( std::cout << bind( &A::i_, arg1) << " " )      );

   return 0;
}

------------------------------------------------

Write the "push_back" for bind/lambda ... you will see why phoenix is so 
much nicer to look at.

michael

-- 
----------------------------------
Michael Caisse
Object Modeling Designs
www.objectmodelingdesigns.com