Re: [boost] [review] Fusion review begins: iterator equal_to doesn't compare values

From: dan marsden (danmarsden_at_[hidden])
Date: 2006-05-10 17:25:02

>On 05/10/2006 03:04 PM, dan marsden wrote:
>> Larry Evans
>>
>>>The boost/fusion/iterator/equal_to.hpp has:
>>>
>>>        operator==(Iter1 const&, Iter2 const&)
>>>        {
>>>            return result_of::equal_to<Iter1, Iter2>::value;
>>>        }
>>>
>>>Obviously only the types are compared and not the values.
>>>Shouldn't the values be compared as well?  I've got my own
>[snip]
>
>> I believe that the position of a fusion iterator must be encoded in
>> the information available at compile. This is needed for fusion sequences
>> to serve as conforming MPL sequences (and probably various other things).
>
>OK, maybe I misunderstood.  I thought that since operator* returns a
>value instead of a type (obviously), that two iterators would be equal
>only when they were the same length and each value returned by operator*
>was equal.  Is that not the case?

I believe 2 fusion iterators should compare equal iff they refer to the same position
within the same sequence. Comparing iterators from different sequences should be
documented to result in undefined behaviour. I'll tighten up the documentation in this
area.

Joel, am I correct in the above?

Cheers
Dan