[Boost-users] boost::transform_iterator, boost::array::iterator and category

Subject: [Boost-users] boost::transform_iterator, boost::array::iterator and category
From: Hicham Mouline (hicham_at_[hidden])
Date: 2009-04-03 07:42:28

Hello,

I have boost::array< pair<double, double>, 16 >::iterator (it has
iterator_traits<>::iterator_category 
random_access_iterator_tag)

which I have transformed with
typedef transform_iterator< UnaryFunction, ... >   iteratorIntoFirst;

struct UnaryFunction: public std::unary_function< pair<double, double>,
double> {
    double operator()( const pair<double, double>& e ) const
    {
      return e.first;
    }
  }

However on asserting the category is still random access, boost static
assert fails:

  BOOST_STATIC_ASSERT((
    boost::is_convertible<
      iteratorIntoFirst,
      std::random_access_iterator_tag
    >::value
  ));

>From the docs
http://www.boost.org/doc/libs/1_38_0/libs/iterator/doc/transform_iterator.ht
ml

If Iterator models Readable Lvalue Iterator and if Iterator models "Random
Access Traversal Iterator", then iterator_category is convertible to
random_access_iterator_tag.

Any ideas,

Regards,