Re: [boost] [range] - Proposal to change the indexed range adaptor

Subject: Re: [boost] [range] - Proposal to change the indexed range adaptor
From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2010-11-01 06:31:59

Den 31-10-2010 21:43, Neil Groves skrev:
> On Sat, Oct 30, 2010 at 6:28 PM, Robert Jones<robertgbjones_at_[hidden]>wrote:
>
>> On Sat, Oct 30, 2010 at 12:38 PM, Neil Groves<neil_at_[hidden]
>>> wrote:
>>
>>>
>>> I propose that a breaking change is made to the index range adaptor so
>> that
>>> it returns a pair<original_reference_type, index_type>.
>>>
>>>
>> Hi Neil
>>
>> Could you provide a use-case example, before and after.
>>
>>
> Certainly. I should have thought to do this in the original email. Thank you
> for taking the time to help me acquire information.
>
> Before:
>
> BOOST_FOREACH( auto item, rng | index )
> {
>      // access to the index is not possible - doh :-(
>      // The return type of the dereferenced element from an index range
> adaptor loses the index
>      const element_type&  elem = item;
> }
>
> After:
>
> BOOST_FOREACH( auto item, rng | indexed )
> {
>       // After my proposed modification, the return type becomes a pair of
> the index
>       // and the original reference type of the underlying iterator/range.
>      std::size i = item.first;
>      const element_type&  elem = item.second;
> }

Your new version works well with foreach, but perhaps less so with
other iteration mathods.

Therefore I suggest that you add a new range instead of messing with the 
old one.

-Thorsten