on Mon Dec 01 2008, Arno Schödl <aschoedl-AT-think-cell.com> wrote:
using std::lower_bound; CustomIt itA, itB; lower_bound( itA, itB );
Do we agree that this is how the client side should work? No, I don't think so. I'm not sure exactly the implications but at first glance it looks too clever by half.
How is that clever? It follows the same pattern as the one for a custom swap:
using std::swap; CustomType tA, tB; swap( tA, tB );
What do you propose instead?
I think if you want to call lower_bound in the most efficient way, it should be possible to do so with qualification. If the algorithm in std:: isn't sufficiently "hookable," one should create a different one that is. The universe of names to be found by ADL should be limited to fundamental operations like swap, since ADL reserves names "globally." I guess if you told me (and I can believe that it's true) that for these other iterators types, the entire implementation of lower_bound needs to be replaced in order to be most efficient, I might have to reconsider lower_bound as a fundamental operation, but it still "feels wrong."
The only way to achieve that, as far as I can see, is to implement a lower_bound for each and every iterator that defines its own partition_point. Or do you have an idea?
You can always provide a CRTP base class template people can use, and implement lower_bound for that.
The reason I used a macro is that CRTP requires that library maintainers are willing to change their code.
Yes, it's an intrusive solution, but implementing lower_bound for a particular iterator type requires knowledge of the implementation details, doesn't it? If you want to be non-intrusive, you can always use traits and tag dispatching or enable_if.
Specifically for my application, you (as maintainer of boost.Iterator?) would have to change boost::transform_iterator/filter_iterator and Joaquin multi_index_container. If we can agree on that, I will change the code to CRTP.
I am willing to consider such changes.
Instead, I could derive from the existing classes and implement CRTP on top, but that creates two versions of each iterator, which is IMO unwarranted if the semantics of the two are the same, the only difference being performance.
Agreed. -- Dave Abrahams BoostPro Computing http://www.boostpro.com