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) && (_MSC_VER >= 1200)
  14 # pragma once
  15 #endif
  16
  17 #include <boost/config.hpp>
  18
  19 #ifdef BOOST_NO_PARTIAL_SPECIALIZATION_IMPLICIT_DEFAULT_ARGS
  20
  21 #define BOOST_RANGE_EXTRACT_OPTIONAL_TYPE( a_typedef )                         \
  22     template< typename C >                                                     \
  23     struct extract_ ## a_typedef                                               \
  24     {                                                                          \
  25         typedef BOOST_DEDUCED_TYPENAME C::a_typedef type;                      \
  26     };
  27
  28 #else
  29
  30 namespace boost {
  31     namespace range_detail {
  32         template< typename T > struct exists { typedef void type; };
  33     }
  34 }
  35
  36 // Defines extract_some_typedef<T> which exposes T::some_typedef as
  37 // extract_some_typedef<T>::type if T::some_typedef exists. Otherwise
  38 // extract_some_typedef<T> is empty.
  39 #define BOOST_RANGE_EXTRACT_OPTIONAL_TYPE( a_typedef )                         \
  40     template< typename C, typename Enable=void >                               \
  41     struct extract_ ## a_typedef                                               \
  42     {};                                                                        \
  43     template< typename C >                                                     \
  44     struct extract_ ## a_typedef< C                                            \
  45     , BOOST_DEDUCED_TYPENAME boost::range_detail::exists< BOOST_DEDUCED_TYPENAME C::a_typedef >::type \
  46     > {                                                                        \
  47         typedef BOOST_DEDUCED_TYPENAME C::a_typedef type;                      \
  48     };
  49
  50 #endif
  51
  52 #endif // include guard