#include <vector>
#include <iterator>
#include <functional>
#include <iostream>
#include <boost/coroutine/coroutine.hpp>
#include <boost/function_output_iterator.hpp>

using namespace std::placeholders;
using boost::coroutines::coroutine;

template <typename T, typename F>
coroutine<T()> outputs_of(F f)
{
    return coroutine<T()>{[f](typename coroutine<T()>::caller_type& caller)
    {
        f(boost::make_function_output_iterator([&caller](const T& t){ caller(t); }));
    }};
}

template <typename InputIterator, typename OutputIterator>
void fun1( InputIterator begin, InputIterator end, OutputIterator out )
{
    // This one multiplies each element by two.
    while (begin != end)
    {
        *out = *begin * 2;
        ++out;
        ++begin;
    }
}

template <typename InputIterator, typename OutputIterator>
void fun2( InputIterator begin, InputIterator end, OutputIterator out )
{
    // This one adds one to each element.
    while (begin != end)
    {
        *out = *begin + 1;
        ++out;
        ++begin;
    }
}

// Wrap fun1 into function object so it's usable with bind()
struct fun1_
{
    template <typename InputIterator, typename OutputIterator>
    void operator()(InputIterator begin, InputIterator end, OutputIterator out) const
    {
        fun1(begin, end, out);
    }
};

int main()
{
    std::vector<int> source = {1, 2, 3, 4};
    
    auto coro = outputs_of<int>(std::bind(fun1_(), source.begin(), source.end(), _1));
    fun2(begin(coro), end(coro), std::ostream_iterator<int>(std::cout, "\n"));
}