Re: [Boost-users] [Iterator] swap and iter_swap do not work with zip_iterator

Subject: Re: [Boost-users] [Iterator] swap and iter_swap do not work with zip_iterator
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2012-07-28 01:51:20

> zip_iterator can be made to model Swappable Iterator (without
> changing its reference_type) by overloading iter_swap for
> zip_iterator as follows:
>
> namespace boost
> {
>     template <typename IteratorTuple>
>     void iter_swap(zip_iterator<IteratorTuple> a, zip_iterator<IteratorTuple> b)
>     {
>         typedef typename zip_iterator<IteratorTuple>::value_type ReferenceTuple;
>         ReferenceTuple ta = *a;
>         ReferenceTuple tb = *b;
>         swap(ta, tb);
>     }
> }
>
> Inserting that snippet above main() in your code, we now get the
> desired output:
>
> 1 2
> 100 200
>
> 2 1
> 200 100
>
> I can't think, off the top of my head, of any reason not to add this
> overload of iter_swap to Boost.

I just realized that, while this will make your example code work
correctly, std::sort will still not work because its implementation
explicitly qualifies calls to iter_swap as std::iter_swap, rather
than making an unqualified call (which would allow the zip_iterator
overload to be found by argument-dependent lookup). (At least, GCC
4.7's implementation of std::sort does this). Is this intentional?

Regards,
Nate