ceph/src/boost/boost/metaparse/v1/optional.hpp

   1 #ifndef BOOST_METAPARSE_V1_OPTIONAL_HPP
   2 #define BOOST_METAPARSE_V1_OPTIONAL_HPP
   3
   4 // Copyright Abel Sinkovics (abel@sinkovics.hu)  2015.
   5 // Distributed under the Boost Software License, Version 1.0.
   6 //    (See accompanying file LICENSE_1_0.txt or copy at
   7 //          http://www.boost.org/LICENSE_1_0.txt)
   8
   9 #include <boost/metaparse/v1/is_error.hpp>
  10 #include <boost/metaparse/v1/accept.hpp>
  11
  12 #include <boost/mpl/if.hpp>
  13
  14 namespace boost
  15 {
  16   namespace metaparse
  17   {
  18     namespace v1
  19     {
  20       template <class P, class Default = void>
  21       struct optional
  22       {
  23         typedef optional type;
  24
  25         template <class S, class Pos>
  26         struct apply :
  27           boost::mpl::if_<
  28             is_error<typename P::template apply<S, Pos> >,
  29             accept<Default, S, Pos>,
  30             // is_error evaluates it anyway
  31             typename P::template apply<S, Pos>::type
  32           >
  33         {};
  34       };
  35     }
  36   }
  37 }
  38
  39 #endif
  40