1 // Copyright (C) 2003, Fernando Luis Cacciola Carballal.
2 // Copyright (C) 2014, 2015 Andrzej Krzemienski.
3 //
4 // Distributed under the Boost Software License, Version 1.0.
5 // (See accompanying file LICENSE_1_0.txt or copy at
6 // http://www.boost.org/LICENSE_1_0.txt)
7 //
8 // See http://www.boost.org/libs/optional for documentation.
9 //
10 // You are welcome to contact the author at:
11 //  fernando_cacciola@hotmail.com
12 //
13 #ifndef BOOST_NONE_17SEP2003_HPP
14 #define BOOST_NONE_17SEP2003_HPP
15 
16 #include "boost/none_t.hpp"
17 
18 // NOTE: Borland users have to include this header outside any precompiled headers
19 // (bcc<=5.64 cannot include instance data in a precompiled header)
20 //  -- * To be verified, now that there's no unnamed namespace
21 
22 namespace boost {
23 
24 #ifdef BOOST_OPTIONAL_USE_OLD_DEFINITION_OF_NONE
25 
26 none_t const none = (static_cast<none_t>(0)) ;
27 
28 #elif defined BOOST_OPTIONAL_USE_SINGLETON_DEFINITION_OF_NONE
29 
30 namespace detail { namespace optional_detail {
31 
32   // the trick here is to make boost::none defined once as a global but in a header file
33   template <typename T>
34   struct none_instance
35   {
36     static const T instance;
37   };
38 
39   template <typename T>
40   const T none_instance<T>::instance = T(); // global, but because 'tis a template, no cpp file required
41 
42 } } // namespace detail::optional_detail
43 
44 
45 namespace {
46   // TU-local
47   const none_t& none = detail::optional_detail::none_instance<none_t>::instance;
48 }
49 
50 #else
51 
52 const none_t none ((none_t::init_tag()));
53 
54 #endif // older definitions
55 
56 } // namespace boost
57 
58 #endif // header guard
59 
60