boost::iterator_range from a templated iterator

Question

I'm trying to write a C++ version of Python's itertools.tee for Boost::Range (as seen here). Here is my first attempt:

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;
}

but as soon as I try to use it:

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);
}

it blows in my face, complaining about a missing value_type in boost::detail::iterator_traits<tee_iterator<std::list<int, std::allocator<int> > > > (and others). What am I missing? Isn't tee_iterator being a child of std::iterator enough?

Answer 1

You forgot to add public:

class tee_iterator : public std::iterator...