Re: [Boost-users] [iterators][range][rangeex] range concatenation

Subject: Re: [Boost-users] [iterators][range][rangeex] range concatenation
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2009-04-06 12:39:52

er skrev:
> Dmitry Vinogradov wrote:
>> Is it possible with Boost (or RangeEx) to concatenate ranges?
>>
>> Sample usage:
>>
>> template <class Range> void process_range(Range const &);
>>
>> std::vector<foo> v = ...;
>> std::list<foo> l = ...;
>> process_range(concat(v, l));
> 
> I take it you have a good reason not to simply copy v and l into a new 
> container. iterator_facade might help, and iterator_range to obtain a 
> range.

It will be impossible to implement a generic iterator that allows
for fast iteration over the two ranges. The problem is that the
iterator would have to check when the new container starts, similar to 
segments in a std::deque<T>.

So I would just call process_range() twice. If you really need to
view the two ranges as one range, then you have to pay an abstraction 
penalty, albeit it might be more efficiant than copying the two 
containers into a new one (and it is probably not that trivial to write 
the iterator that depends on two or more other iterator types).

If "foo" is a heavy object, then copying the references of the elements
to a new container std::vector<boost::reference_wrapper<foo>> is 
probably the most efficient alternative.

-Thorsten