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, but in the meantime here's the general idea: - outputs_of(f) creates a coroutine c whose body calls f with an output iterator which yields the outputted value - begin() of the resulting range starts the coroutine and saves the first yielded value - dereference() of the begin iterator returns the saved value - increment() of the begin iterator re-enters the coroutine and saves the next yielded value - when the coroutine is finished a flag is set to that the begin and end iterators return true Hope that helps! Regards, Nate