[boost] Re: range_result_iterator

From: Eric Niebler (eric_at_[hidden])
Date: 2005-05-04 12:18:03

Peter Dimov wrote:
> David Abrahams wrote:
> 
>> "Peter Dimov" <pdimov_at_[hidden]> writes:
>>
>>> Thorsten Ottosen wrote:
>>>
>>>> I guess the design could havebeen that way; but we don't say
>>>> container< const T >::iterator to get container<T>::const_iterator.
>>>
>>>
>>> Isn't range_iterator<R>::type the iterator type of the range R?
>>
>>
>> Yes, in a world where iterator and const_iterator are distinguished. 
>> [...]
> 
> 
> My question is to be read as follows:
> 
> Is it not the design intent of range_iterator<R>::type to give the 
> iterator type of the range R, so that I can write:
> 
> template<class R> void f( R & r )
> {
>    typename range_iterator<R>::type i = r.begin();
> }
> 
> and hence, is it not perfectly logical for it to return 
> C::const_iterator for R == C const?
> 
> It was meant to support your point.

My understanding of the current design is that this is the purpose of 
range_result_iterator, so I would rewrite your code as:

template<class R> void f( R & r )
{
    typename range_result_iterator<R>::type i = r.begin();
}

range_iterator always evaluates to R::iterator regardless of the 
const-ness of R, and range_const_iterator always evaluates to 
R::const_iterator.

In my experience with Boost.Range, I have found range_result_iterator to 
be useful. I have found little need for range_iterator and 
range_const_iterator. YMMV.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com