on Mon Jul 27 2009, Maxim Yanchenko <maximyanchenko-AT-yandex.ru> wrote:
David Abrahams <dave <at> boostpro.com> writes:
Then how would you safely implement
find[_f-1,_e]( range, x );
At first glance, you can't. Is there a known use case for that? If not, it's moot.
Who knows. Maybe you want the element before the found one to be there for some reason.
"Maybe, for some reason" arguments don't hold much water with me, especially in a library design context.
Say I have an array of prices active now on exchange. In my algorithm, I come up with some price, and now I want to place my orders 5 levels above and 5 levels below the price I need. With iterators (omitting boundary cases) this would be:
it = find( prices.begin(), prices.end(), desired_price ); desired_levels = boost::range( it-5, it+5 ); place_orders( desired_levels );
With the syntax above, what I need is find[_f-5, _f+5](range, x).
There can be more examples if this kind, say fancy smoothing an image, when you need to find a pixel and then smooth it over neighbor pixels. Same in numerical calculations on grids - you often take neighbors of what you found into account.
My point is not that there are no use cases, it's that there may be reasonably simple ways of expressing these less-common use cases that don't intrude on the interface of find itself, but instead combine find with some orthogonal components. -- Dave Abrahams BoostPro Computing http://www.boostpro.com