Re: [Boost-users] chaining ouput iterator to input iterator

Subject: Re: [Boost-users] chaining ouput iterator to input iterator
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2012-07-08 01:18:20

> I have a function that transforms a serie of numbers into another serie:
>
> template <typename InputIterator, typename OutputIterator>
> void transform( InputIterator begin, InputIterator end, OutputIterator out )
> {
> }
>
>
> and a 2nd function that calculates the standard deviation of a sample
>
> template <typename InputIterator >
> double stdev( InputIterator begin, InputIterator end)
> {
> }
>
> Is there a way to chain these existing functions in order to get the std dev
> of the transformed serie, without storing the intermediate numbers?
> Maybe with the help of some lazy iterator, or some lazy function?

In this particular case, you can use boost::transform_iterator rather
than std::transform, as Jeff pointed out.

However, this does not resolve the problem in general, which is how to 
treat the sequence of values a function writes to an output iterator as
a range (or pair of iterators) input to another function (without
accumulating the elements in a container, of course).

This seems like a textbook use case for coroutines. I wonder whether a
solution using Boost.Context would impose sufficiently little overhead
to provide a general solution to this problem.

Regards,
Nate