//

 // Boost.Pointer Container

 //

 //  Copyright Thorsten Ottosen 2003-2005. Use, modification and

 //  distribution is subject to the Boost Software License, Version

 //  1.0. (See accompanying file LICENSE_1_0.txt or copy at

 //  http://www.boost.org/LICENSE_1_0.txt)

 //

 // For more information, see http://www.boost.org/libs/ptr_container/

 //

 #ifndef BOOST_INDIRECT_CONTAINER_NULLABLE_HPP

 #define BOOST_INDIRECT_CONTAINER_NULLABLE_HPP

 #if defined(_MSC_VER) && (_MSC_VER >= 1200)

 # pragma once

 #endif

 #include <boost/type_traits/detail/yes_no_type.hpp>

 #include <boost/mpl/eval_if.hpp>

 #include <boost/mpl/identity.hpp>

 #include <boost/config.hpp>

 namespace boost

 {

     template< class T >

     struct nullable

     {

         typedef T type;

     };   

     namespace ptr_container_detail

     {

         template< class T >

         type_traits::yes_type is_nullable( const nullable<T>* );

         type_traits::no_type is_nullable( ... );        

     }

     template< class T >

     struct is_nullable

     {

     private:

             BOOST_STATIC_CONSTANT( T*, var );

     public:

             BOOST_STATIC_CONSTANT(bool, value = sizeof( ptr_container_detail::is_nullable( var ) ) 

                                                 == sizeof( type_traits::yes_type ) );

     };

     template< class T >

     struct remove_nullable

     {

         typedef BOOST_DEDUCED_TYPENAME mpl::eval_if< is_nullable<T>,

                                                       T,

                                             mpl::identity<T> >::type

             type;

     };

 }

 #endif