Indeed, as long as the range does not escape, everything is fine. But here we are in trouble: some_stacked_adaptor_range<...> rng( make_difference_range( vecnA, vecnB ) ); Again, notation makes no difference, but Neil's idea, which I fully endorse, namely easy stacking, makes the problem all the more apparent: some_stacked_adaptor_range<...> rng( vecnA | difference( vecnB ) ); // wrong What makes this really annoying is that there is an easy way out: Wouldn't it be more natural to represent a forward range as a single iterator, with an extra .at_end() check? This would eliminate the problem, because a difference_range would only need two such iterators, not four. Stacking them naively would have 2^N storage growth, rather than 4^N, and we still don't need to worry about range lifetime. For other classes of iterators, the situation is similar. bidirectional ranges have at_end() and at_begin(), and random_access_ranges a size() and an operator[]. I know that overthrowing such an established concept as ranges is not terribly popular, but I don't see any other way to combine easy stacking with no worry about lifetimes. Arno -----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Giovanni Piero Deretta Sent: Friday, August 29, 2008 3:28 PM To: boost@lists.boost.org Subject: Re: [boost] lifetime of ranges vs. iterators On Fri, Aug 29, 2008 at 3:13 PM, Arno Schödl <aschoedl@think-cell.com> wrote:
I have seen your | operator. It is o.k. for unary things, like rng | filter( predicate ), but for binary things, it is a bit weird:
rngA | difference(rngB)
I find the alternatives clearer: rngA - rngB would be nice (but requires concept checking), or difference( rngA, rngB ).
What about Infix a-la FC++? (rngA ^difference^ rngB) I love the syntax, but maybe this is too much operator abuse.
But regardless of notation, doesn't this suffer from the same problem that these objects are temporaries?
I'm still missing something: where is the problem in: vector<int> vecnA; vector<int> vecnB; DoSomethingWithRangeThatStoresIterators( difference_range< int, int > diffrng( vecnA, vecnB ) ); This works, as long as the range doesn't escape from DSWRTSI, or a copy is made. [of course a make_difference_range would make the code much cleaner] -- gpd _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost -- Dr. Arno Schoedl · aschoedl@think-cell.com Technical Director think-cell Software GmbH · Invalidenstr. 34 · 10115 Berlin, Germany http://www.think-cell.com · phone +49-30-666473-10 · toll-free (US) +1-800-891-8091 Directors: Dr. Markus Hannebauer, Dr. Arno Schoedl · Amtsgericht Charlottenburg, HRB 85229