cpp-rotate/rotate.hpp

#include <vector>
#include <cstdlib>
#include <boost/preprocessor.hpp>

template <typename T, typename I, I T::*mem>
struct access {
  using value_type = I;
  using access_type = T;
  
  value_type& get(access_type& t) const { return t.*mem; }
  value_type const& get(access_type const& t) const { return t.*mem; }
};

template <typename T, typename...Members>
class rotate;

template <typename T, typename...Members> class proxy;

template <typename T, typename Member>
class rotate<T, Member> {
public:
  using value_type = typename Member::value_type;
  using data_type = std::vector<value_type>;
  
  value_type&       get(size_t n, Member) { return rotated_.at(n); }
  value_type const& get(size_t n, Member) const { return rotated_.at(n); }
  
  data_type const&  get(Member) const { return rotated_; }

protected:
  void push_back(T const& t) {
    rotated_.push_back(Member().get(t));
  }

private:
  data_type rotated_;
};

template <typename T, typename Member0, typename...Members>
class rotate<T, Member0, Members...> : public rotate<T, Member0>, public rotate<T, Members...> {
public:
  proxy<T, Member0, Members...> get(size_t n);

  void push_back(T const& t) {
    rotate<T, Member0>::push_back(t);
    rotate<T, Members...>::push_back(t);
  }
  
  using rotate<T, Member0>::get;
  using rotate<T, Members...>::get;
};

#define PROXY_ELEMENT(T, elem) decltype(T::elem)& elem
#define PROXY_MEMBER(r, T, elem) PROXY_ELEMENT(T, elem);
#define PROXY_CONSTR(r, T, elem) BOOST_PP_CAT(PROXY_ELEMENT(T, elem),_),
#define PROXY_INIT(r, T, elem) elem(BOOST_PP_CAT(elem,_)),
#define PROXY_SET(r, t, elem) t.elem = elem;

#define proxy_t(T, mseq) proxy<T BOOST_PP_SEQ_FOR_EACH(ROTATE_ACCESS, T, mseq)>

#define ROTATE_PROXY(T, mseq) \
  template<> class proxy_t(T, mseq) { \
  public: \
    proxy(BOOST_PP_SEQ_FOR_EACH(PROXY_CONSTR, T, mseq) bool) \
    : BOOST_PP_SEQ_FOR_EACH(PROXY_INIT, T, mseq) dummy(false) {} \
    \
    explicit operator T() const { \
      T t; \
      BOOST_PP_SEQ_FOR_EACH(PROXY_SET, t, mseq) \
      return t; \
    } \
    \
    BOOST_PP_SEQ_FOR_EACH(PROXY_MEMBER, T, mseq) \
    bool dummy; \
  }

#define ROTATE_ACCESS(r, T, elem) ,access_t(T, elem)
#define PROXY_ASSIGN(r, T, elem) rotate<T, access_t(T, elem)>::get(n, access_t(T, elem)()),

#define rotate_t(T, mseq) rotate<T BOOST_PP_SEQ_FOR_EACH(ROTATE_ACCESS, T, mseq)>
#define access_t(T, M) access<T, decltype(T::M), &T::M>

//#define DEFINE_ROTATE_NAME(name, T, mseq) \
//  using name = rotate_t(T, mseq); \
//  ROTATE_PROXY(T, mseq); \
//  template <typename T, typename M0, typename...Ms> \
//  proxy<T, M0, Ms...> rotate<T, M0, Ms...>::get(size_t n) { \
//    return proxy<T, M0, Ms...>{BOOST_PP_SEQ_FOR_EACH(PROXY_ASSIGN, T, mseq) false}; \
//  }

#define DEFINE_ROTATE_NAME(name, T, mseq) \
  ROTATE_PROXY(T, mseq); \
  class name : public rotate_t(T, mseq) { \
  public:\
    proxy_t(T, mseq) get(size_t n) { \
    return proxy_t(T, mseq){BOOST_PP_SEQ_FOR_EACH(PROXY_ASSIGN, T, mseq) false}; \
    } \
    using rotate_t(T, mseq)::get; \
  }

#define DEFINE_ROTATE(T, mseq) DEFINE_ROTATE_NAME(T##_rotate, T, mseq)

//#include <iostream>
//
//struct particle {
//  int x, y, dx, dy;
//  char color;
//};
//
//DEFINE_ROTATE(particle, (color)(x)(y)(dx)(dy))
//
//int main(int argc, char const *argv[]) {
//  (void) argc;
//  (void) argv;
//  particle p{0, 0, 0, 0, 0};
//  particle_rotate pr;
//  pr.push_back(p);
//
//  {
//    proxy<particle> pp = pr.get(0);
//    pp.x = 5;
//  }
//
//  {
//    proxy<particle> pp = pr.get(0);
//    std::cout << pp.x << std::endl;
//    particle copy = particle(pp);
//    std::cout << copy.x << std::endl;
//  }
//  
//  return 0;
//}