ceph/src/boost/libs/range/include/boost/range/detail/extract_optional_type.hpp

   1 // Boost.Range library
   2 //
   3 //  Copyright Arno Schoedl & Neil Groves 2009.
   4 //  Use, modification and distribution is subject to the Boost Software
   5 //  License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   6 //  http://www.boost.org/LICENSE_1_0.txt)
   7 //
   8 // For more information, see http://www.boost.org/libs/range/
   9 //
  10 #ifndef BOOST_RANGE_DETAIL_EXTRACT_OPTIONAL_TYPE_HPP_INCLUDED
  11 #define BOOST_RANGE_DETAIL_EXTRACT_OPTIONAL_TYPE_HPP_INCLUDED
  12
  13 #if defined(_MSC_VER)
  14 # pragma once
  15 #endif
  16
  17 #include <boost/config.hpp>
  18 #include <boost/preprocessor/cat.hpp>
  19 #include <boost/mpl/has_xxx.hpp>
  20
  21 #if !defined(BOOST_MPL_CFG_NO_HAS_XXX)
  22
  23 // Defines extract_some_typedef<T> which exposes T::some_typedef as
  24 // extract_some_typedef<T>::type if T::some_typedef exists. Otherwise
  25 // extract_some_typedef<T> is empty.
  26 #define BOOST_RANGE_EXTRACT_OPTIONAL_TYPE( a_typedef )                          \
  27     BOOST_MPL_HAS_XXX_TRAIT_DEF(a_typedef)                                      \
  28     template< typename  C, bool B = BOOST_PP_CAT(has_, a_typedef)<C>::value >   \
  29     struct BOOST_PP_CAT(extract_, a_typedef)                                    \
  30     {};                                                                         \
  31     template< typename C >                                                      \
  32     struct BOOST_PP_CAT(extract_, a_typedef)< C, true >                         \
  33     {                                                                           \
  34         typedef BOOST_DEDUCED_TYPENAME C::a_typedef type;                       \
  35     };
  36
  37 #else
  38
  39 #define BOOST_RANGE_EXTRACT_OPTIONAL_TYPE( a_typedef )                          \
  40     template< typename C >                                                      \
  41     struct BOOST_PP_CAT(extract_, a_typedef)                                    \
  42     {                                                                           \
  43         typedef BOOST_DEDUCED_TYPENAME C::a_typedef type;                       \
  44     };
  45
  46 #endif
  47
  48 #endif // include guard