Re: [Boost-users] [multi_array] Useful algorithms (from Re: Multi_array: A "proper" iterator over a N>1 Multi_array?)

From: Beth Jacobson (bethj_at_[hidden])
Date: 2006-05-17 16:21:57

Antonio Piccolboni wrote:

> As I said in a former message that I am afraid fell through the
> cracks, sorry if I am repeating myself, I don't think rewriting the
> whole STL algorithm lib for multi_array is a solution. for_each,
> accumulate, sort, where do we stop? I recently needed to apply random
> shuffle, for instance. I think the solution is to define iterators
> that provide a "flat", element by element view of a multi_array. These
> iterators would be regular skip iterators that just a have a fancy
> increment operation that looks at the stride vector to decide by how
> much to jump when incremented.

I agree that would be the ideal solution, but the multi_array-specific 
algorithms have one big advantage that kind of iterator: they already 
exist.

> I've been using data() and data()+num_elements for the same purpose,
> but that breaks for non contiguos storage (that is, not guaranteed to
> work for views)

That's exactly the issue that these algorithms address. They accept 
regular multi_arrays, subarrays, and views and handle them all correctly.

> 
> I don't think rewriting all the algorithms for multi_array is a viable
> strategy, nor is in keeping  with the idea that data structures and
> algorithms should be made as ortogonal as reasonably possible.  Just
> my 2c
> 

I agree in theory, but I'm not familiar enough either with the 
multi_array library or template programming in general to tackle the job 
of writing the iterator myself. If you or someone else has definite 
plans to do it, I won't bother with a Wiki page for the algorithms, but 
if the iterator is likely to remain theoretical for the foreseeable 
future, it still seems worthwhile to offer a working, though imperfect 
solution for general use. Jeff Garland described Wiki contributions as 
"certainly not up to the usual Boost standards, but useful 
none-the-less." The algorithms don't meet Boost standards for the 
reasons you described, but I think they conform well to the "useful 
none-the-less" standard required for the Wiki.

Regards,
Beth