Re: [boost] Cycle Iterator Adapter (was: Re: Help with iterator helpers)

From: nbecker_at_[hidden]
Date: 2002-02-01 08:41:37

Sorry, I realize I should clarify this.  The problem is the 
desired behaviour of a cirular container is ambiguous.  If I tell you
to copy (a, b, c), and a > b (base iterator), what do I really want?
The interpretation I used is that I want you to iterate starting at a
and continuing to b.  This means that 

distance (a, b) = (b - a) >= 0 ? (b - a) : (b - a + sizeof
(container))

However, I can see that  a different interpretation is also valid.
With this interpretation, the distance (a, b) is signed, and in this
case we can only use data from 1/2 of the container at a time.  In
other words, copy (a, b, c) would only be able to copy at most 1/2 of
the container.

Note that if you do nothing, and inherit the default policy, you will
get neither of these behaviours.  You get a behaviour that I think is
not useful.

I think in most cases it is the first behaviour that I would want from
my circular containters.  This means that I know when I write 
copy (a, b, c), that b is always logically ahead of a.