i have these 2 functions provided to me and I wonder whether they can somehow be chained without using intermediary memory?
No. You have to supply a range [begin..end) for fun2(), so this range should be prepared first.
someone mentioned boost.coroutine could help in this case?
I'm the one who mentioned that, and yes, it is possible :)
Basically, one can use coroutines to implement a generic outputs_of() function that takes a unary function whose argument is an output iterator, and returns a range representing all the values passed to this output iterator, without storing them all.
You would call it like this:
fun2(outputs_of(bind(fun1, input, _1)), output)
I actually wrote such a function, but using an earlier version of the coroutine library (back when the coroutine functionality was still in Boost.Context). I am planning to update my implementation after the interface of Boost.Coroutine is stabilized (it is currently under review on the dev list). I am happy to post it once I've done that
Turns out that the final version of Boost.Coroutine that made it into the 1.53 release has out-of-the-box support for treating the values returned by a coroutine as a range, which makes writing such an outputs_of() function trivial: 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); })); }}; } A complete example using the two functions in your original post is attached. The code uses some C++11 features like lambdas, but these can easily be translated to their C++03 equivalents if necessary. I'll leave it to you as an exercise to do that if you need to. Hope that helps! Regards, Nate