On 11/12/2013 8:38 AM, Thorsten Ottosen wrote:
On 12-11-2013 16:41, Eric Niebler wrote:
I've now built a filter_range, transform_range, and an istream_range in this vein. Initial results are looking promising, but I haven't benchmarked performance, yet. A commenter on my blog claims to have benchmarked perf of istream_range, with good results, which is encouraging.
If anybody wants to take a peek, you can find the code here:
https://github.com/ericniebler/range-v3
I'm making no effort to maintain source compatibility, going instead with the design that seems right to me for C++11.
Good. I totally agree that r-value refs change things completely.
Some small comments (applies for transform_range as well):
A. For filter_range, you should inherit from the predicate if possible to enable EBO. I don't know if lambdas complicate this?
I should use EBO, but that's not the right place for it. It adds a bunch of associated namespaces to the filter_range type. Rather, the predicate and the adapted range should be in a compressed pair. I have this working locally already. The space savings are worth it: a filtered, filtered, transformed range goes from 24 bytes to 16.
B. For the constructor
filter_range(Rng && rng, Pred pred)
then maybe it would be beneficial that empty predicates are constructed via
filter_range(Rng && rng)
? I guess it needs benchmarking though, but the compiler will have to elide a series of moves vs. default construct an empty class.
I don't think this is worth it. I can't imaging any compiler having a hard time eliminating empty moves. There's nothing to move!
C. I can't quite figure out your use of filterer::filterer1. Do you really have to store the predicate here also?
filterer1 is the object returned by "filter" in an expression like this: vec | filter(pred) So yes, it needs to store the pred. One of my breaking changes is to allow the "filter" name to be reused such that these two are equivalent: vec | filter(pred) filter(vec, pred) I want this. I never liked "filtered" or the adaptors namespace. -- Eric Niebler Boost.org http://www.boost.org