Re: [boost] [range][iterator] contiguous iterators

Subject: Re: [boost] [range][iterator] contiguous iterators
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2013-03-19 11:18:33

On 19-03-2013 15:23, Stefan Strasser wrote:
> Am 19.03.2013 14:07, schrieb Thorsten Ottosen:
>>> going back to my example of database.get, you might wanna use it to load
>>> image data into a large container,
>>
>> No problem here.
>
> right.
>
>>
>>> or use it to load 4 byte into an
>>> integer.
>>
>> Hm. How would that work? What concepts do you have in mind? Do yo want
>> to interpret an int as a container of 4 bytes?
>
> no, not as part of what I'm proposing to be added to Boost.Range. it was
> an example only.
>
> the point is that there are many algorithms that you don't want to only
> be able to output into containers, as you've suggested using push_back,
> but into anything, using an OutputIterator. like copy().
>
> but there are cases you can't use a regular OutputIterator for
> efficiency reasons, because the result has to be a bulk call to
> std::memcpy if that's possible, not iterating one by one.
>
> so instead of writing a generic function:
> template<class OutputIterator> //'char' value type
> void load(OutputIterator);
>
> you are forced to use
>
> template<class Container>
> void load(Container &);
>
> for performance reasons. which you don't want, see above.
> please see my original email for how I'm suggesting to solve this.
>
>
> even copy() could benefit from this, e.g.:
>
> copy(Range const &r,OutputIterator out){
>      copy(r,out,category of out);
> }
>
> copy(Range const &r,OutputIterator out,range_output_iterator_tag){
>      *out=r;
> }
>
> "out" can now copy the whole range at once, using vector.reserve(). or
> sputn() it into a file without buffering. or whetever else.
> (for that, it needs is_contiguous<>)

It appears to me that you can just do that by implementing a wrapper 
class that enables you to call boost::push_back. If its too contrieved 
to use push_back, we may add a function called write:

template< class OutPutRange, class Rng >
OutPutRange& write( OutPutRange& to, const Rng& from )
{ to.write( from ); return to; }

Anyway, I guess its possible to define an "output range", but it does 
not seem desirable stick it into the existing interface for output 
iterators, does it?

-Thorsten