來自模板迭代器的boost :: iterator_range

Question

我想爲Boost :: Range編寫Python的itertools.tee的C++版本（如所見here）。這是我第一次嘗試：

template<typename R> 
class tee_iterator : std::iterator<std::forward_iterator_tag, typename boost::range_value<R>::type> 
{ 
public: 
    typedef typename boost::range_value<R>::type T; 
    typedef std::list<T> tee_queue; 
    typedef std::vector<tee_queue> tee_queue_collection; 

    tee_iterator(const R& r, tee_queue* q, tee_queue_collection* qs) : 
     it_(r.begin()), queue_(q), queues_(qs) {} 

    tee_iterator(const R& r) : it_(r.end()), queue_(NULL), queues_(NULL) {} 

    T& operator*() const { return current_; } 

    tee_iterator& operator++() 
     { 
      if (queue_->empty()) { 
       ++it_; 
       for (auto q : queues_) { 
        q->push_back(*it_); 
       } 
      } 
      current_ = queue_->front(); 
      queue_->pop_front(); 
      return *this; 
     } 

    bool operator==(tee_iterator const& o) const { return it_ == o.it_; } 
    bool operator!=(tee_iterator const& o) const { return !(*this == o); } 

private: 
    typedef typename boost::range_iterator<const R>::type const_iterator; 
    const_iterator it_; 
    tee_queue* queue_; 
    tee_queue_collection* queues_; 
    T current_; 
}; 

template<typename R> 
using tee_range = boost::iterator_range<tee_iterator<R> >; 

template<typename R> 
std::list<tee_range<R> > tee(const R& r, int n) 
{ 
    typedef typename boost::range_value<R>::type T; 
    typedef std::list<T> tee_queue; 
    typedef std::vector<tee_queue> tee_queue_collection; 

    tee_queue_collection queues(n); 
    std::list<tee_range<R> > ranges; 
    for (int i = 0; i < n; ++i) { 
     tee_range<R> t = { tee_iterator<R>(r, &queues[i], &queues), tee_iterator<R>(r) }; 
     ranges.push_back(t); 
    } 
    return ranges; 
} 

但只要我嘗試使用它：

int main(int argc, char* argv[]) 
{ 
    std::list<int> l; 
    for (int i = 0; i < 10; ++i) { 
     l.push_back(i); 
    } 
    auto t = tee(l, 3); 
} 

它吹在我的臉上，在抱怨boost::detail::iterator_traits<tee_iterator<std::list<int, std::allocator<int> > > >丟失value_type（及其他）。我錯過了什麼？ tee_iterator是不是std::iterator足夠的孩子？

Answer 1

你忘了添加public：

class tee_iterator : public std::iterator...