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
22namespace boost {
23
24#ifdef BOOST_OPTIONAL_USE_OLD_DEFINITION_OF_NONE
25
26none_t const none = (static_cast<none_t>(0)) ;
27
28#elif defined BOOST_OPTIONAL_USE_SINGLETON_DEFINITION_OF_NONE
29
30namespace 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
45namespace {
46 // TU-local
47 const none_t& none = detail::optional_detail::none_instance<none_t>::instance;
48}
49
50#else
51
52const none_t none ((none_t::init_tag()));
53
54#endif // older definitions
55
56} // namespace boost
57
58#endif // header guard
59
60