src/helpers/song_iterator_maker.h

   1 /***************************************************************************
   2  *   Copyright (C) 2008-2016 by Andrzej Rybczak                            *
   3  *   electricityispower@gmail.com                                          *
   4  *                                                                         *
   5  *   This program is free software; you can redistribute it and/or modify  *
   6  *   it under the terms of the GNU General Public License as published by  *
   7  *   the Free Software Foundation; either version 2 of the License, or     *
   8  *   (at your option) any later version.                                   *
   9  *                                                                         *
  10  *   This program is distributed in the hope that it will be useful,       *
  11  *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
  12  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
  13  *   GNU General Public License for more details.                          *
  14  *                                                                         *
  15  *   You should have received a copy of the GNU General Public License     *
  16  *   along with this program; if not, write to the                         *
  17  *   Free Software Foundation, Inc.,                                       *
  18  *   51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.              *
  19  ***************************************************************************/
  20
  21 #ifndef NCMPCPP_HELPERS_SONG_ITERATOR_MAKER_H
  22 #define NCMPCPP_HELPERS_SONG_ITERATOR_MAKER_H
  23
  24 #include <boost/iterator/transform_iterator.hpp>
  25 #include "menu.h"
  26 #include "song_list.h"
  27
  28 template <typename SongT>
  29 struct SongPropertiesExtractor
  30 {
  31         template <typename ItemT>
  32         auto &operator()(ItemT &item) const
  33         {
  34                 return m_cache.assign(&item.properties(), &item.value());
  35         }
  36
  37 private:
  38         mutable SongProperties m_cache;
  39 };
  40
  41 template <typename IteratorT>
  42 SongIterator makeSongIterator(IteratorT it)
  43 {
  44         typedef SongPropertiesExtractor<
  45                 typename IteratorT::value_type::Type
  46                 > Extractor;
  47         static_assert(
  48                 std::is_convertible<
  49                   typename std::result_of<Extractor(typename IteratorT::reference)>::type,
  50                   SongProperties &
  51                 >::value, "invalid result type of SongPropertiesExtractor");
  52         return SongIterator(boost::make_transform_iterator(it, Extractor{}));
  53 }
  54
  55 template <typename ConstIteratorT>
  56 ConstSongIterator makeConstSongIterator(ConstIteratorT it)
  57 {
  58         typedef SongPropertiesExtractor<
  59                 typename ConstIteratorT::value_type::Type
  60                 > Extractor;
  61         static_assert(
  62                 std::is_convertible<
  63                   typename std::result_of<Extractor(typename ConstIteratorT::reference)>::type,
  64                   const SongProperties &
  65                 >::value, "invalid result type of SongPropertiesExtractor");
  66         return ConstSongIterator(boost::make_transform_iterator(it, Extractor{}));
  67 }
  68
  69 #endif // NCMPCPP_HELPERS_SONG_ITERATOR_MAKER_H