Re: [boost] Boost range - Add variadic join/zip

Subject: Re: [boost] Boost range - Add variadic join/zip
From: Neil Groves (neil_at_[hidden])
Date: 2013-05-10 04:37:53

>
> However, boost's zip_iterators are not writable. I don't really think it
> would be possible to make them writable, but that would allow code like
> this:

<snip>
</snip>

>
> template<class C, class D, class... Args>
> auto join(C&& c, D&& d, Args&&... args)
> ->
>
> decltype(boost::join(boost::join(boost::make_iterator_range(std::forward<C>(c)),
>
> boost::make_iterator_range(std::forward<D>(d))),
>                         join(std::forward<Args>(args)...))) {
>   return
> boost::join(boost::join(boost::make_iterator_range(std::forward<C>(c)),
>
>  boost::make_iterator_range(std::forward<D>(d))),
>                      join(std::forward<Args>(args)...));
> }
>
> A variadic zip is more complicated. If we want write access we cannot use
> boost zip_iterator. Still one can use Anthony Williams' TupleIterator:
>
> template <class... T>
> auto zip(T&&... c)
> -> boost::iterator_range<
>
> decltype(iterators::makeTupleIterator(std::begin(std::forward<T>(c))...))>
> {
>   return boost::make_iterator_range
>       (iterators::makeTupleIterator(std::begin(std::forward<T>(c))...),
>        iterators::makeTupleIterator(std::end(std::forward<T>(c))...));
> }
>
> For read-only access one could use boost::zip_iterator, but I think
> write-access is _really_ important (e.g. sort wouldn't work).
>
> Would it be possible to add similar functionality to boost range?
>
>
Yes and I shall do so when I find time. If you find time to create a patch
it would be even quicker of course, but I understand if this is not
possible. It seems we are all running with less and less time to work on
these extra-curricula projects!

> This code wouldn't work without the help of everyone who participated in
> the following SO discussions:
> -
>
> http://stackoverflow.com/questions/14366576/boostrangejoin-for-multiple-ranges
> -
>
> http://stackoverflow.com/questions/13840998/sorting-zipped-locked-containers-in-c-using-boost-or-the-stl
> and without Anthony Williams's tupleIterator. See also
> http://www.justsoftwaresolutions.co.uk/articles/pair_iterators.pdf
>
>
I'll have to see if I can persuade Anthony to be charitable enough to allow
us to include his tuple iterator. Ideally this would be made a public
feature of Boost.Iterator I think.

> Bests,
> Gonzalo BG
>

Thank you for your feedback. It's great to have positive suggestions that
are actionable like this.

Regards,
Neil Groves