[boost] iterator adaptors and const correctness

From: Neal D. Becker (nbecker_at_[hidden])
Date: 2004-11-10 14:01:22

I was struggling with const correctness and iterator adaptors.  At first I was 
using iterator_facade.  I found it difficult to get dereference to work 
correctly.  After changing to iterator_adaptor I got things working.  I'm 
wondering if the approach I used is "correct".

I include the whole class here, because it isn't really very big.

I was using a Ring class which contains an iterator, which is
cycle_iterator<std::vector<Complex>::iterator>.

If a Ring const& is passed I had problems with dereference.

The changes I made to cycle_iterator fix this were:

1) Add templated conversion constructor to cycle_iterator, to allow implicit 
conversion of cycle_iterator -> const cycle_iterator.

2) Include both 

reference dereference()

and

const reference dereference() const

(likewise for operator[])

So, do my changes constitute a "correct" approach to making interoperable 
iterators using boost::iterator_adaptor?