[boost] Re: Library proposal --- pair (and tuple) iterators

From: David Abrahams (dave_at_[hidden])
Date: 2003-09-22 07:27:22

Anthony Williams <anthony.williamsNOSPAM_at_[hidden]> writes:

> David Abrahams <dave_at_[hidden]> writes:
>> Anthony Williams <anthony.williamsNOSPAM_at_[hidden]> writes:
>
>>> I would like to submit my "pair iterators" library for inclusion in
>>> boost. The library is described in my article "Pairing off Iterators" from
>>> Overload 51, which is available at
>>> http://cplusplus.anthonyw.cjb.net/pair_iterators.pdf
>
>> I think you may be a little late.  Have you seen
>> http://www.boost-consulting.com/boost/boost/iterator/zip_iterator.hpp
>> ??
>
> I hadn't. But then, you only checked it in two weeks ago. Does it work
> correctly with things like this?
>
> template<typename It>
> void rotate_by_one(It begin,It end)
> {
>     typedef std::iterator_traits<It>::value_type ValueType;
>
>     if(begin==end)
>     {
>         return;
>     }
>     ValueType value=*begin; // take a copy and keep it around
>     
>     for(It prev=begin++;begin!=end;++begin,++prev)
>     {
>         *prev=*begin; // overwrite the value copied
>     }
>     *prev=value; // use the copy
> }
>
> *that* was the bit that I found hardest to get working --- having a value type
> such that *it was a real reference, writing to *it updated the underlying
> iterators, yet copying from *it produced an object of the same type that
> *didn't* update the underlying iterators.

The above code would work, but *it is not a real reference and
doesn't need to be.  In fact, I'm pretty sure that would make the
iterator bigger and slower than neccessary.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com