Re: [boost] [range] fat iterators?

On 11/12/2013 10:44 AM, Daniel James wrote:

On 12 November 2013 17:13, Eric Niebler wrote:

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On 11/12/2013 8:21 AM, Evgeny Panasyuk wrote:

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12.11.2013 19:41, Eric Niebler:

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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.

While new "slim" istream_range is faster than version with "fat" iterators, it is still not the fastest possible. In particular, it does two comparisons per cycle iteration: one is "!rng_->next()", and another is comparison of iterators, like "it != last". <snip>

The commenter on my blog claims this extra check is optimized away by a smart compiler like gcc. He says[^1]:

Regardless of efficiency, a range adaptor could make implementing input and forward ranges much easier.

Agreed. I've implemented such an adaptor, but I'm not yet happy with it so I haven't committed it yet. I think we can take a page out of Boost.Iterator's book and have range_adaptor and range_facade. With some thought, we should have a good answer for the folks who just want to write something like the D range interface. -- Eric Niebler Boost.org http://www.boost.org