[cfe-dev] [patch] [libc++] missing difference_type in advance implementation

[Gonzalo BG]

Thanks for adding the section.

I've tried hard to come up with a MWE that is simpler than this, but I've
failed. This is the simplest thing I've been able to come up with. As you
can see, the code works fine for random access iterators, but fails for
bidirectional and forward iterators (see the errors below in the comments):

#include <algorithm>
#include <boost/iterator/counting_iterator.hpp>
// From https://github.com/gnzlbg/arithmetic_type :
#include <arithmetic_type/arithmetic_type.hpp>

int main() {
  /// Opaque Integer without implicit conversions:
  struct tag {};
  using Int = arithmetic::Arithmetic<int, tag>;

  /// Works as expected
  boost::counting_iterator<Int, boost::random_access_traversal_tag, Int>
a(Int{10});
  std::advance(a, Int{5});

  /// Fails: libcxx/iterator:458:13: error: invalid operands to
  ///   binary expression ('typename
  ///   iterator_traits<counting_iterator<Arithmetic<int, tag>,
  ///   bidirectional_traversal_tag, Arithmetic<int, tag> >
>::difference_type'
  ///   (aka 'arithmetic::Arithmetic<int, tag>') and 'int')
  /// if (__n >= 0)
  ///     ~~~ ^  ~
  boost::counting_iterator<Int, boost::bidirectional_traversal_tag, Int>
b(Int{10});
  std::advance(b, Int{5});

  /// Fails: libcxx/iterator:449:16: error: invalid operands to binary
  ///   expression ('typename
iterator_traits<counting_iterator<Arithmetic<int, tag>,
  ///   forward_traversal_tag, Arithmetic<int, tag> > >::difference_type'
(aka
  ///   'arithmetic::Arithmetic<int, tag>') and 'int')
  /// for (; __n > 0; --__n)
  ///        ~~~ ^ ~
  boost::counting_iterator<Int, boost::forward_traversal_tag, Int>
c(Int{10});
  std::advance(c, Int{5});
}



On Thu, Apr 3, 2014 at 5:20 AM, Marshall Clow <mclow.lists at gmail.com> wrote:

> On Mar 22, 2014, at 8:45 AM, Marshall Clow <mclow.lists at gmail.com> wrote:
>
> > P.P.S.        I’ll take a look at adding info to the libc++ web page.
>
> I’ve added a section to http://libcxx.llvm.org about reporting bugs and
> contributing patches
>
> — Marshall
>
>
>
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