boost/ptr_container/nullable.hpp

   1 //
   2 // Boost.Pointer Container
   3 //
   4 //  Copyright Thorsten Ottosen 2003-2005. Use, modification and
   5 //  distribution is subject to the Boost Software License, Version
   6 //  1.0. (See accompanying file LICENSE_1_0.txt or copy at
   7 //  http://www.boost.org/LICENSE_1_0.txt)
   8 //
   9 // For more information, see http://www.boost.org/libs/ptr_container/
  10 //
  11
  12
  13 #ifndef BOOST_INDIRECT_CONTAINER_NULLABLE_HPP
  14 #define BOOST_INDIRECT_CONTAINER_NULLABLE_HPP
  15
  16 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  17 # pragma once
  18 #endif
  19
  20 #include <boost/type_traits/detail/yes_no_type.hpp>
  21 #include <boost/mpl/eval_if.hpp>
  22 #include <boost/mpl/identity.hpp>
  23 #include <boost/config.hpp>
  24
  25 namespace boost
  26 {
  27
  28     template< class T >
  29     struct nullable
  30     {
  31         typedef T type;
  32     };
  33
  34     namespace ptr_container_detail
  35     {
  36         template< class T >
  37         type_traits::yes_type is_nullable( const nullable<T>* );
  38
  39         type_traits::no_type is_nullable( ... );
  40     }
  41
  42     template< class T >
  43     struct is_nullable
  44     {
  45     private:
  46             BOOST_STATIC_CONSTANT( T*, var );
  47     public:
  48
  49 #if BOOST_WORKAROUND(BOOST_MSVC, >= 1400)
  50 #pragma warning(push)
  51 #pragma warning(disable:6334)
  52 #endif
  53
  54             BOOST_STATIC_CONSTANT(bool, value = sizeof( ptr_container_detail::is_nullable( var ) )
  55                                                 == sizeof( type_traits::yes_type ) );
  56 #if BOOST_WORKAROUND(BOOST_MSVC, >= 1400)
  57 #pragma warning(pop)
  58 #endif
  59
  60     };
  61
  62     template< class T >
  63     struct remove_nullable
  64     {
  65         typedef BOOST_DEDUCED_TYPENAME mpl::eval_if< is_nullable<T>,
  66                                                       T,
  67                                             mpl::identity<T> >::type
  68             type;
  69     };
  70
  71 }
  72
  73 #endif