cpp-rotate/include/rotate/rotate.hpp

#pragma once
#include <vector>
#include <cstdlib>
#include <boost/preprocessor/seq/for_each.hpp>

namespace data {
  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>;
  
  inline value_type&       get(size_t n, Member)       { return rotated_.at(n); }
  inline value_type const& get(size_t n, Member) const { return rotated_.at(n); }
  
  inline 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);
  template <typename...Proxied> proxy<T, Proxied...> getp(size_t n);

  inline 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(T, elem) BOOST_PP_CAT(PROXY_ELEMENT(T, elem),_)
#define PROXY_CONSTR_J(r, T, elem) , PROXY_CONSTR(T, elem)
#define PROXY_INIT(T, elem) elem(BOOST_PP_CAT(elem,_))
#define PROXY_INIT_J(r, T, elem) , PROXY_INIT(T, elem)
#define PROXY_SET(r, t, elem) t.elem = elem;
#define PROXY_RSET(r, t, elem) elem = t.elem;

#define proxy_t(T, mseq) proxy<T, rotate_members(T, mseq)>

#define ROTATE_PROXY(T, mseq) \
  template<> class proxy_t(T, mseq) { \
  public: \
    proxy(PROXY_CONSTR(T, BOOST_PP_SEQ_HEAD(mseq)) \
      BOOST_PP_SEQ_FOR_EACH(PROXY_CONSTR_J, T, BOOST_PP_SEQ_TAIL(mseq))) \
    : PROXY_INIT(T, BOOST_PP_SEQ_HEAD(mseq)) \
      BOOST_PP_SEQ_FOR_EACH(PROXY_INIT_J, T, BOOST_PP_SEQ_TAIL(mseq)) \
    { \
    } \
    \
    proxy & operator=( T const & obj ) { \
      BOOST_PP_SEQ_FOR_EACH(PROXY_RSET, obj, mseq) \
      return *this; \
    } \
    \
    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) \
  }

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

#define rotate_members(T, mseq) ROTATE_ACCESS(T, BOOST_PP_SEQ_HEAD(mseq)) \
  BOOST_PP_SEQ_FOR_EACH(ROTATE_ACCESS_J, T, BOOST_PP_SEQ_TAIL(mseq))
#define rotate_t(T, mseq) rotate<T, rotate_members(T, mseq)>
#define access_t(T, M) data::access<T, decltype(T::M), &T::M>

//#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){ \
//        PROXY_ASSIGN(T, BOOST_PP_SEQ_HEAD(mseq)) \
//        BOOST_PP_SEQ_FOR_EACH(PROXY_ASSIGN_J, T, BOOST_PP_SEQ_TAIL(mseq)) \
//      }; \
//    } \
//    using rotate_t(T, mseq)::get; \
//  }

#define DEFINE_ROTATE_NAME(name, T, mseq) \
  ROTATE_PROXY(T, mseq); \
  using name##_proxy = proxy_t(T, mseq); \
  template <> \
  proxy_t(T, mseq) rotate_t(T, mseq)::get(size_t n) { \
    return proxy_t(T, mseq){ \
      PROXY_ASSIGN(T, BOOST_PP_SEQ_HEAD(mseq)) \
      BOOST_PP_SEQ_FOR_EACH(PROXY_ASSIGN_J, T, BOOST_PP_SEQ_TAIL(mseq)) \
    }; \
  } \
  using name = rotate_t(T, mseq)

#define DEFINE_PROXY_NAME( name, T, mseq ) \
  ROTATE_PROXY( T, mseq ); \
  using name = proxy_t( T, mseq );

#define DEFINE_PROXY_CONVERSION(T, mseq1, mseq2) \
  template <> \
  template <> \
  proxy_t(T, mseq2) rotate_t(T, mseq1)::getp(size_t n) { \
    return proxy_t(T, mseq2){ \
      PROXY_ASSIGN(T, BOOST_PP_SEQ_HEAD(mseq2)) \
      BOOST_PP_SEQ_FOR_EACH(PROXY_ASSIGN_J, T, BOOST_PP_SEQ_TAIL(mseq2)) \
    }; \
  }

#define DEFINE_ROTATE(T, mseq) \
  using T##_proxy = proxy_t(T, mseq); \
  DEFINE_ROTATE_NAME(T##_rotate, T, mseq)