boost/mpl/aux_/erase_impl.hpp

   1
   2 #ifndef BOOST_MPL_AUX_ERASE_IMPL_HPP_INCLUDED
   3 #define BOOST_MPL_AUX_ERASE_IMPL_HPP_INCLUDED
   4
   5 // Copyright Aleksey Gurtovoy 2000-2004
   6 //
   7 // Distributed under the Boost Software License, Version 1.0.
   8 // (See accompanying file LICENSE_1_0.txt or copy at
   9 // http://www.boost.org/LICENSE_1_0.txt)
  10 //
  11 // See http://www.boost.org/libs/mpl for documentation.
  12
  13 // $Id$
  14 // $Date$
  15 // $Revision$
  16
  17 #include <boost/mpl/clear.hpp>
  18 #include <boost/mpl/push_front.hpp>
  19 #include <boost/mpl/reverse_fold.hpp>
  20 #include <boost/mpl/iterator_range.hpp>
  21 #include <boost/mpl/next.hpp>
  22 #include <boost/mpl/aux_/na.hpp>
  23
  24 namespace boost { namespace mpl {
  25
  26 // default implementation; conrete sequences might override it by
  27 // specializing either the 'erase_impl' or the primary 'erase' template
  28
  29 template< typename Tag >
  30 struct erase_impl
  31 {
  32     template<
  33           typename Sequence
  34         , typename First
  35         , typename Last
  36         >
  37     struct apply
  38     {
  39         typedef typename if_na< Last,typename next<First>::type >::type last_;
  40
  41         // 1st half: [begin, first)
  42         typedef iterator_range<
  43               typename begin<Sequence>::type
  44             , First
  45             > first_half_;
  46
  47         // 2nd half: [last, end) ... that is, [last + 1, end)
  48         typedef iterator_range<
  49               last_
  50             , typename end<Sequence>::type
  51             > second_half_;
  52
  53         typedef typename reverse_fold<
  54               second_half_
  55             , typename clear<Sequence>::type
  56             , push_front<_,_>
  57             >::type half_sequence_;
  58
  59         typedef typename reverse_fold<
  60               first_half_
  61             , half_sequence_
  62             , push_front<_,_>
  63             >::type type;
  64     };
  65 };
  66
  67 }}
  68
  69 #endif // BOOST_MPL_AUX_ERASE_IMPL_HPP_INCLUDED