#include <boost/mpl/empty_base.hpp>
#include <boost/mpl/fold.hpp>
#include <boost/mpl/inherit.hpp>
#include <boost/mpl/vector.hpp>
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/control/expr_if.hpp>
#include <boost/preprocessor/repetition/enum.hpp>
#include <boost/preprocessor/repetition/enum_params.hpp> 

template<typename T>
class variable_list_member
{
public:
        T& get()     {return t;}
  const T& get()const{return t;}

private:
  T t;
};

template<typename Sequence>
class variable_list_seq:
  protected boost::mpl::fold<
    Sequence,
    boost::mpl::empty_base,
    boost::mpl::inherit<
      boost::mpl::_1,
      variable_list_member<boost::mpl::_2>
    >
    >::type
{
public:
  template<typename T>
  T& get()
  {
    return static_cast<variable_list_member<T>&>(*this).get();
  }

  template<typename T>
  const T& get()const
  {
    return static_cast<const variable_list_member<T>&>(*this).get();
  }
};

/* front end to variable_list_seq hiding the use of MPL sequences */

#define VARIABLE_LIST_TEMPLATE_PARM(z,n,var) \
  typename BOOST_PP_CAT(var,n) BOOST_PP_EXPR_IF(n,=boost::mpl::na)

template<BOOST_PP_ENUM(10,VARIABLE_LIST_TEMPLATE_PARM,T)>
class variable_list:
  public variable_list_seq<boost::mpl::vector<BOOST_PP_ENUM_PARAMS(10,T)> >
{
};

#undef VARIABLE_LIST_TEMPLATE_PARM

/**************** testing ****************/

#include <boost/mpl/vector.hpp>
#include <iostream>

int main()
{
  typedef variable_list<int,char,double> vl_type;

  vl_type        v;
  const vl_type& vc=v;

  v.get<int>()=5;
  v.get<char>()='a';
  v.get<double>()=1.0;

  std::cout<<"v.get<int>()=="<<vc.get<int>()<<std::endl;
  std::cout<<"v.get<char>()=="<<vc.get<char>()<<std::endl;
  std::cout<<"v.get<double>()=="<<vc.get<double>()<<std::endl;
}