Subject: Re: [boost] [range] fat iterators?
From: TONGARI J (tongari95_at_[hidden])
Date: 2013-11-07 22:59:38
2013/11/7 Eric Niebler <eniebler_at_[hidden]>
> I wrote an article describing the "fat" std::istream_iterator and how it
> can be slimmed down by giving it an owning istream_range. I see there
> already is an istream_range in Boost.Range, but it suffers from the
> fat-iterator problem I describe there. Is there a compelling reason why
> the implementation of boost::istream_range shouldn't be changed to be
> more like the one I describe? Also, as a commented pointed out, the same
> problem exists for the filtered range and the transformed range, too.
> The trick, of course, will be keeping intermediate temporary ranges
> alive long enough to avoid lifetime issues when we chain adaptors and
> assign the result to a local variable. I think a range library that's
> sensitive to the value category of range objects and makes copies of
> rvalue ranges would solve this problem. Thoughts?
> Is it time for Boost.Range 3.0?
> : http://ericniebler.com/2013/11/07/input-iterators-vs-input-ranges
That reminds me of the question I asked years ago (no one answered):
Surely all approaches have tradeoffs...
About the lifetime problem, could it be solved(?) with the approach Fusion
used? (i.e. the distinction between 'view' & 'sequence').
I'm willing to have a reusable range, rather than a disposable one.
The problem of a disposable one also described in my question.
And I wonder, if we could have 2-phase construction.
phase 1: A lazy range builder w/o begin/end
phase 2: A range w/ begin/end and probably do some work at construction, as
And there have to be a trait like:
typedef Range& type;
And specialized for those have 2 phases.
To implement the algorithms:
void some_algo(Range const& rng, ...)
typename range_type<Range const>::type r(rng);
some_algo(begin(r), end(r), ...);
For range adaptors, they also store phase 1 object, and make the underlying
phase 2 object on the fly.
What do you think?
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