ceph/src/boost/libs/spirit/include/boost/spirit/home/x3/support/traits/variant_find_substitute.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2014 Joel de Guzman
   3     http://spirit.sourceforge.net/
   4
   5     Distributed under the Boost Software License, Version 1.0. (See accompanying
   6     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7 =============================================================================*/
   8 #if !defined(BOOST_SPIRIT_X3_VARIANT_FIND_SUBSTITUTE_APR_18_2014_930AM)
   9 #define BOOST_SPIRIT_X3_VARIANT_FIND_SUBSTITUTE_APR_18_2014_930AM
  10
  11 #include <boost/spirit/home/x3/support/traits/is_substitute.hpp>
  12
  13 namespace boost { namespace spirit { namespace x3 { namespace traits
  14 {
  15     template <typename Variant, typename Attribute>
  16     struct variant_find_substitute
  17     {
  18         // Get the type from the variant that can be a substitute for Attribute.
  19         // If none is found, just return Attribute
  20
  21         typedef Variant variant_type;
  22         typedef typename variant_type::types types;
  23         typedef typename mpl::end<types>::type end;
  24
  25         typedef typename
  26             mpl::find_if<types, is_same<mpl::_1, Attribute> >::type
  27         iter_1;
  28
  29         typedef typename
  30             mpl::eval_if<
  31                 is_same<iter_1, end>,
  32                 mpl::find_if<types, traits::is_substitute<mpl::_1, Attribute> >,
  33                 mpl::identity<iter_1>
  34             >::type
  35         iter;
  36
  37         typedef typename
  38             mpl::eval_if<
  39                 is_same<iter, end>,
  40                 mpl::identity<Attribute>,
  41                 mpl::deref<iter>
  42             >::type
  43         type;
  44     };
  45
  46     template <typename Variant>
  47     struct variant_find_substitute<Variant, Variant>
  48         : mpl::identity<Variant> {};
  49
  50 }}}}
  51
  52 #endif