toast/iterator/first_iterator.hpp

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#ifndef toast_iterator_first_iterator_hpp_INCLUDED
#define toast_iterator_first_iterator_hpp_INCLUDED

#include <iterator>
#include <boost/iterator/transform_iterator.hpp>
#include <toast/traits/pair_ref_traits.hpp>

namespace toast {

namespace detail {

template <typename Iterator>
struct get_first
{
  typedef typename std::iterator_traits<Iterator>::reference pair_reference;
  typedef typename pair_ref_traits<pair_reference>::first_type& result_type;
  result_type operator()(pair_reference pair) const { return pair.first; }
};

} // namespace detail

template <typename Iterator>
class first_iterator
  : public boost::transform_iterator<detail::get_first<Iterator>, Iterator>
{
public:
  explicit first_iterator(Iterator i)
    : boost::transform_iterator<detail::get_first<Iterator>, Iterator>
  (boost::make_transform_iterator(i, detail::get_first<Iterator>())) {}
};

template <typename Iterator>
first_iterator<Iterator> make_first_iterator(Iterator i)
{
  return first_iterator<Iterator>(i);
}

} // namespace toast

#endif // toast_iterator_first_iterator_hpp_INCLUDED

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