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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 |