Geometry Boost List: [ggl] pre-/post-increment op on iterators

Subject: [ggl] pre-/post-increment op on iterators
From: Mateusz Loskot (mateusz)
Date: 2009-04-29 16:09:34

Barend Gehrels wrote:
> 
>>> A related question, I've created some iterators recently and it would
>>> be convenient to have an interator on a vector which has a segment as
>>> its valuetype. Didn't work it out and don't know if it is possible at
>>> all, do you think it makes sense here?
>>
>> I'm not sure I can grasp the idea.
>> Perhaps you could illustrate your idea with a snippet of code?
>>
>> I can see vector that has a segment as its value_type as
>> simple as vector<segment>, but it is not what you're thinking of,
>> I presume.
>
> OK, let's try, it should look like something like this:
> 
> vector<point_2d> line;
> // ... file this line somehow
> // creates iterator which should iterator over the whole line
> ggl::segment_iterator<vector<point_2d>::const_iterator> it(line);
> // indicates the end
> ggl::segment_iterator<vector<point_2d>::const_iterator> end(line.end());
> while(it != end)
> {
>    ggl::segment<const point_2d> segment = *it;
>    std::cout << length(segment) << std::endl;
>    it++;
> }
> 
> So operator * returns a segment, valuetype should be a segment-type (can
> be specified as template par), operator-> should work on a segment, etc.
> It would be instead of having two iterators, I've often prev and it,
> where prev=it++;

Have you solve it? If not, I can give it a try.

I think it can be solved with a thin iterator adapter that
dereferences to segment, instead of to point.
The adapter, or a view as called in some situations, should do the job.

Best regards
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org