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

    49                                                 == sizeof( type_traits::yes_type ) );

    50     };

    51     

    52     template< class T >

    53     struct remove_nullable

    54     {

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

    56                                                       T,

    57                                             mpl::identity<T> >::type

    58             type;

    59     };

    60 

    61 }

    62 

    63 #endif