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From: Pavol Droba (droba_at_[hidden])
Date: 2005-03-14 02:29:40


On Sun, Mar 13, 2005 at 10:04:05PM -0800, Eric Niebler wrote:
> Background:
> I have been working on range-based algorithms and adaptors. The
> algorithms are variants of the std::algorithms that accept ranges
> instead of a [begin,end) iterator pair. The adaptors are like the
> iterator adaptors, except they adapt ranges.
> Following the principal of least surprise, I want to call my range
> adaptors filter_range, indirect_range, reverse_range and transform_range
> (to parallel filter_iterator, indirect_iterator, etc). But I can't do
> this, because there already is a transform_range, and it's a function!
> Problem:
> At the bottom of iterator_range.hpp is this:
> template< typename SeqT, typename Range, typename FuncT >
> inline SeqT transform_range( const Range& r, FuncT Func )
> {
> SeqT Seq;
> std::transform( begin( r ), end( r ),
> std::back_inserter(Seq), Func );
> return Seq;
> }
> I'm not sure why. It looks like a range-based algorithm, but ... why
> provide only one? (Two actually -- copy_range is there also.) And why
> call it transform_range() instead of just calling it "transform" and
> making it part of a complete range-based algorithm library?
> Solution:
> I suggest the functions copy_range() and transform_range() should be
> removed or moved into a "deprecated" namespace, freeing up the
> identifier "boost::transform_range" to be a type, analagous to
> boost::transform_iterator. Development should proceed on a range-based
> algorithms library to fill the need that the existing
> "transform_range()" function is meeting.
> Thoughts?

Originaly I was the author of iterator_range class and the utilities.
It was then taken to Boost.Range library as a more meaningful place.

Rantionale for these two functions was to improve the usability of
iterator_range class.

transform_range is not so crucial, but the copy_range is very important.
Without it you cannot easily convert iterator_range to a string for
instance. You need to go through iterator-constructor.

So instead of


You need to write
str=std::string(aRange.begin(), aRange.end());

The second one is not as nice, but what is more important, it disallows
you to pass a range by value in a chain. In other words, you cannot


To sumarize, copy_range is an essential utility, that provides a way of
copying between different range types, especialy the legacy ones like
std::string. Therefor it has an important place in the Boost.Range



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