text: /* Copyright 2003-2013 Joaquin M Lopez Munoz.
   * Distributed under the Boost Software License, Version 1.0.
   * (See accompanying file LICENSE_1_0.txt or copy at
   * http://www.boost.org/LICENSE_1_0.txt)
   *
   * See http://www.boost.org/libs/multi_index for library home page.
   */
  
  #ifndef BOOST_MULTI_INDEX_DETAIL_NO_DUPLICATE_TAGS_HPP
  #define BOOST_MULTI_INDEX_DETAIL_NO_DUPLICATE_TAGS_HPP
  
  #if defined(_MSC_VER)
  #pragma once
  #endif
  
  #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
  #include <boost/mpl/fold.hpp>
  #include <boost/mpl/set/set0.hpp>
  
  namespace boost{
  
  namespace multi_index{
  
  namespace detail{
  
  /* no_duplicate_tags check at compile-time that a tag list
   * has no duplicate tags.
   * The algorithm deserves some explanation: tags
   * are sequentially inserted into a mpl::set if they were
   * not already present. Due to the magic of mpl::set
   * (mpl::has_key is contant time), this operation takes linear
   * time, and even MSVC++ 6.5 handles it gracefully (other obvious
   * solutions are quadratic.)
   */
  
  struct duplicate_tag_mark{};
  
  struct duplicate_tag_marker
  {
    template <typename MplSet,typename Tag>
    struct apply
    {
      typedef mpl::s_item<
        typename mpl::if_<mpl::has_key<MplSet,Tag>,duplicate_tag_mark,Tag>::type,
        MplSet
      > type;
    };
  };
  
  template<typename TagList>
  struct no_duplicate_tags
  {
    typedef typename mpl::fold<
      TagList,
      mpl::set0<>,
      duplicate_tag_marker
    >::type aux;
   
    BOOST_STATIC_CONSTANT(
      bool,value=!(mpl::has_key<aux,duplicate_tag_mark>::value));
  };
  
  /* Variant for an index list: duplication is checked
   * across all the indices.
   */
  
  struct duplicate_tag_list_marker
  {
    template <typename MplSet,typename Index>
    struct apply:mpl::fold<
      BOOST_DEDUCED_TYPENAME Index::tag_list,
      MplSet,
      duplicate_tag_marker>
    {
    };
  };
  
  template<typename IndexList>
  struct no_duplicate_tags_in_index_list
  {
    typedef typename mpl::fold<
      IndexList,
      mpl::set0<>,
      duplicate_tag_list_marker
    >::type aux;
   
    BOOST_STATIC_CONSTANT(
      bool,value=!(mpl::has_key<aux,duplicate_tag_mark>::value));
  };
  
  } /* namespace multi_index::detail */
  
  } /* namespace multi_index */
  
  } /* namespace boost */
  
  #endif
  