Re: [boost] [range] Is it conceivable to have it extended?

boost::iterator_range is a great concept/class but it does not seem to play efficiently with certain input sequences and seem to be too strong a requirement for certain algorithms. I have an old-fashioned C string in mind (I am sure there are other examples) and traversing algorithms.

When I tried deploying boost::iterator_range for string-to-int conversion purposes, I quickly realized that I was traversing the string twice -- first to find the end and second to do the work.

What I think is missing is the "parent" concept of a "sequence". Say,

template struct sequence { iterator_type begin(); sentry_type sentry(); };

Then "range" would implement and refine the "sequence" concept by

template struct range : sequence { iterator_type begin(); iterator_type end(); sentry_type sentry() { return end; } }

I.e., as "range" implements/is the "sequence", the boost::iterator_range will have one additional "useless" sentry() method.

That way all the old code (using and/or needing end()) would still work but traversing algorithms might gradually adapt to only require "sequences" instead of "ranges":

template Function for_each(Iterator beg, Sentry sentry, Function fun) { for (; beg != sentry; ++beg) fun(*beg); return fun; }

That means that now all "open-ended" (with no known "end") "ranges" (they are not even "ranges" in the strict meaning of the word but rather "sequences") can be handled efficiently.

I ended up having such an "extended" range in Boost.Convert (to handle C string traversals efficiently) but I hate having/maintaining the code and much prefer the standard solution.

Eric Niebler ran into the same problem and came up with a solution more or less along the same lines: an Iterable concept which generalizes a Range, which has begin and end iterators of potentially different types [1]. My understanding is that Eric plans to present a library implementing his approach at the next C++ standards committee meeting in November. Regards, Nate [1] http://ericniebler.com/2014/02/21/introducing-iterables/