Re: [boost] [filesystem] C++11 range-based for statement and BOOST_FOREACH support

Subject: Re: [boost] [filesystem] C++11 range-based for statement and BOOST_FOREACH support
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2012-07-21 00:11:21

> >> > Hm.
> >> >
> >> > Why not follow this design:
> >> >
> >> > http://www.boost.org/doc/libs/1_50_0/libs/range/doc/html/range/reference/ranges/istream_range.html
> >>
> >> The implementation would be more elegant, but the user would have to write:
> >>
> >> BOOST_FOREACH(directory_entry& x, directory_range(directory_iterator(".")))
> >>
> >> instead of the simpler:
> >>
> >> BOOST_FOREACH(directory_entry& x, directory_iterator("."))
> >>
> >> I verified the above with an actual implementation and test.
> >
> > I don't see why that's the case. In the posted link, the function istream_range()
> > takes an argument of type istream&, which is the same argument type that the
> > constructor of istream_iterator takes. Notice that istream_range() does *not*
> > take an actual istream_iterator as its constructor argument.
> >
> > Similarly, I would expect directory_range() to take a path argument, and return
> > something like make_iterator_range(directory_iterator(p), directory_iterator()).
>
> The make_iterator_range template requires ForwardIterators, but
> directory_iterator only meets InputIterator requirements. Perhaps
> someone familiar with Boost.Range can come up with a workaround.

istream_iterator is not a forward iterator either, yet istream_range() returns an
iterator_range<istream_iterator>. The documentation for iterator_range says:

"If the template argument is not a model of Forward Traversal Iterator, one can 
still use a subset of the interface.
          In particular, size()
          requires Random Access 
Traversal Iterators whereas empty() only requires Single Pass Iterators."

So it seems this should be OK.

Regards,
Nate