Re: [boost] Date iterators in Boost Date-Time

From: Jeff Garland (jeff_at_[hidden])
Date: 2003-08-12 06:47:56

On Tue, 12 Aug 2003 10:44:45 +1000, Chris Trengove wrote
> The date iterators in Boost Date-Time appear to be designed to 
> support iteration forward in time, being modelled on the STL 
> InputIterator. However, at times it is convenient to iterate 
> backwards in time, and the temptation is just to use something like
> 
> day_iterator ditr(date,-1);
> ++ditr;
> 
> that is; specify a negative "offset" as the optional construction parameter
> which all four of the iterators provide.

Yep.  This has come up several times before...

> This works for all of the provided iterators except the 
> month_iterator, and it wouldn't be too difficult to make that one 
> work as well (by providing a subtract() method for the wrapping_int2 
> template used in the implementation).

Another user has submitted a change to me, that hasn't made it into
the library, that performs the equivalent by modifying adjust_functors.hpp.
Looking back on the history of the number of requests on this it looks like
it should be a priority to officially support this option.  Or perhaps, even
better, to step up and support bi-directional or random access iterators.

> Are there any other issues involved in providing this support for backwards
> iteration?

No, it appears not, but if you do this make sure to write some tests to be sure...

Jeff