//Purpose:
//  Answer question in post:
//
//    http://article.gmane.org/gmane.comp.lib.boost.user/62386
//
//References:
//  [ffold]
//    http://www.boost.org/doc/libs/1_44_0/libs/fusion/doc/html
//      /fusion/algorithm/iteration/functions/fold.html
//
#include <boost/fusion/algorithm/iteration/fold.hpp>
#include <boost/fusion/algorithm/transformation/join.hpp>
#include <boost/fusion/container/vector.hpp>
#include <boost/fusion/sequence/io.hpp>
#include <boost/utility/result_of.hpp>

#include <iostream>

struct join_ftor
/**@brief
 *  Forward decl of functor for joining 2 fusion sequences.
 */
;
namespace boost
{
  template
  < typename LhSequence
  , typename RhSequence
  >
struct result_of
  < join_ftor(LhSequence const,RhSequence const)
  >
  /**@brief
   *  As specified by table 1.37 Requirement for Parameter f 
   *  in [ffold].
   */  
: fusion::result_of::join<LhSequence const, RhSequence const>
{
};

}//exit boost namespace
        
struct join_ftor
/**@brief
 *  modified from 'struct make_string' from [ffold].
 */
{
    template<typename LhSequence, typename RhSequence>
      typename boost::result_of<join_ftor(LhSequence const,RhSequence const)>::type
    operator()(LhSequence const& lhs, RhSequence const& rhs)const
    {
        return boost::fusion::join(lhs,rhs);
    }
};

template<typename T,unsigned Index=0>
struct tu
{
    tu(T a_t):my_t(a_t){}
    T my_t;
    
        friend
      std::ostream&
    operator<<
      ( std::ostream& sout
      , tu const& x
      )
    {
        sout<<"tu<"<<Index<<">("<<x.my_t<<")";
        return sout;
    } 
};

using namespace boost;

int main(void)
{
    fusion::vector<> state0;
    typedef fusion::vector<tu<int>, tu<char>, tu<double> > t0;
    t0 v0(100,'b',300.1);
    typedef fusion::vector<tu<int,1>, tu<char,1>, tu<double,1> > t1;
    t1 v1(100,'b',300.1);
    std::cout<<"v0="<<v0<<"\n";
    std::cout<<"v1="<<v1<<"\n";
    fusion::vector<t0,t1> vv(v0,v1);
    join_ftor joiner;
    auto fold_vv=fusion::fold(vv,state0,joiner);
    std::cout
      <<"fold(vv,state0,join_ftor())="
      <<fold_vv
      <<"\n";
    return 0;
}