Boost.Coroutineでフィボナッチ + itertoolsっぽい(?)drop

co_fibo.cpp

/*
 * C++11 (VisualStudio 2013 Express Edition)
 * boost 1.55.0
 */

#include <iostream>
#include <boost/coroutine/all.hpp>
#include <boost/range/irange.hpp>
#include <boost/multiprecision/cpp_int.hpp>

template<typename T>
class fibo {
  T pre_;
  T current_;
  typedef typename boost::coroutines::coroutine<T>::pull_type pull_type;
  typedef typename boost::coroutines::coroutine<T>::push_type push_type;
  typedef typename boost::coroutines::pull_coroutine<T> generator;
  fibo() : pre_(T(0)), current_(T(1)){}
public:
  void operator()(push_type& yield){
    for (;;){
      yield(current_);
      pre_ += current_;
      std::swap(pre_, current_);
    }
  }
  static generator generate(){
    return pull_type(fibo<T>());
  }
};

template<typename T>
class itertools {
  typedef typename boost::coroutines::pull_coroutine<T>::iterator iterator;
public:
  static iterator drop(const int n, iterator& it){
    for (int i = 0; i < n; ++i, ++it);
    return it;
  }
};


void fibo_int(){
  std::cout << "-- fibo<int> --" << std::endl;

  typedef itertools<int> itts;

  auto gen = fibo<int>::generate();
  auto it = itts::drop(10, boost::begin(gen));

  for (int i : boost::irange(10, 21)){
    std::cout << i << " : " << *(it++) << std::endl;
  }
}

void fibo_bigint(){
  std::cout << "-- fibo<bigint> --" << std::endl;

  typedef boost::multiprecision::cpp_int bigint;
  typedef itertools<bigint> itts;

  auto gen = fibo<bigint>::generate();
  auto it = itts::drop(100, boost::begin(gen));

  for (int i : boost::irange(100, 111)){
    std::cout << i << " : " << *(it++) << std::endl;
  }
}

int main(){
  fibo_int();
  fibo_bigint();
  return 0;
}