ceph/src/boost/libs/geometry/include/boost/geometry/util/compress_variant.hpp

   1 // Boost.Geometry (aka GGL, Generic Geometry Library)
   2
   3 // Copyright (c) 2007-2015 Barend Gehrels, Amsterdam, the Netherlands.
   4 // Copyright (c) 2008-2015 Bruno Lalande, Paris, France.
   5 // Copyright (c) 2009-2015 Mateusz Loskot, London, UK.
   6
   7 // This file was modified by Oracle on 2015.
   8 // Modifications copyright (c) 2015, Oracle and/or its affiliates.
   9
  10 // Contributed and/or modified by Menelaos Karavelas, on behalf of Oracle
  11
  12 // Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
  13 // (geolib/GGL), copyright (c) 1995-2010 Geodan, Amsterdam, the Netherlands.
  14
  15 // Use, modification and distribution is subject to the Boost Software License,
  16 // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
  17 // http://www.boost.org/LICENSE_1_0.txt)
  18
  19 #ifndef BOOST_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP
  20 #define BOOST_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP
  21
  22
  23 #include <boost/mpl/equal_to.hpp>
  24 #include <boost/mpl/fold.hpp>
  25 #include <boost/mpl/front.hpp>
  26 #include <boost/mpl/if.hpp>
  27 #include <boost/mpl/insert.hpp>
  28 #include <boost/mpl/int.hpp>
  29 #include <boost/mpl/set.hpp>
  30 #include <boost/mpl/size.hpp>
  31 #include <boost/mpl/vector.hpp>
  32 #include <boost/variant/variant_fwd.hpp>
  33
  34
  35 namespace boost { namespace geometry
  36 {
  37
  38
  39 namespace detail
  40 {
  41
  42 template <typename Variant>
  43 struct unique_types:
  44     boost::mpl::fold<
  45         typename boost::mpl::reverse_fold<
  46             typename Variant::types,
  47             boost::mpl::set<>,
  48             boost::mpl::insert<
  49                 boost::mpl::placeholders::_1,
  50                 boost::mpl::placeholders::_2
  51             >
  52         >::type,
  53         boost::mpl::vector<>,
  54         boost::mpl::push_back
  55             <
  56                 boost::mpl::placeholders::_1, boost::mpl::placeholders::_2
  57             >
  58     >
  59 {};
  60
  61 template <typename Types>
  62 struct variant_or_single:
  63     boost::mpl::if_<
  64         boost::mpl::equal_to<
  65             boost::mpl::size<Types>,
  66             boost::mpl::int_<1>
  67         >,
  68         typename boost::mpl::front<Types>::type,
  69         typename make_variant_over<Types>::type
  70     >
  71 {};
  72
  73 } // namespace detail
  74
  75
  76 /*!
  77     \brief Meta-function that takes a boost::variant type and tries to minimize
  78         it by doing the following:
  79         - if there's any duplicate types, remove them
  80         - if the result is a variant of one type, turn it into just that type
  81     \ingroup utility
  82     \par Example
  83     \code
  84         typedef variant<int, float, int, long> variant_type;
  85         typedef compress_variant<variant_type>::type compressed;
  86         typedef boost::mpl::vector<int, float, long> result_types;
  87         BOOST_MPL_ASSERT(( boost::mpl::equal<compressed::types, result_types> ));
  88
  89         typedef variant<int, int, int> one_type_variant_type;
  90         typedef compress_variant<one_type_variant_type>::type single_type;
  91         BOOST_MPL_ASSERT(( boost::equals<single_type, int> ));
  92     \endcode
  93 */
  94
  95 template <typename Variant>
  96 struct compress_variant:
  97     detail::variant_or_single<
  98         typename detail::unique_types<Variant>::type
  99     >
 100 {};
 101
 102
 103 }} // namespace boost::geometry
 104
 105
 106 #endif // BOOST_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP