| 1 | // Copyright (C) 2003, Fernando Luis Cacciola Carballal. |
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| 2 | // Copyright (C) 2014, 2015 Andrzej Krzemienski. |
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| 3 | // |
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| 4 | // Distributed under the Boost Software License, Version 1.0. |
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| 5 | // (See accompanying file LICENSE_1_0.txt or copy at |
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| 6 | // http://www.boost.org/LICENSE_1_0.txt) |
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| 7 | // |
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| 8 | // See http://www.boost.org/libs/optional for documentation. |
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| 9 | // |
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| 10 | // You are welcome to contact the author at: |
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| 11 | // fernando_cacciola@hotmail.com |
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| 12 | // |
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| 13 | #ifndef BOOST_NONE_17SEP2003_HPP |
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| 14 | #define BOOST_NONE_17SEP2003_HPP |
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| 15 | |
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| 16 | #include "boost/config.hpp" |
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| 17 | #include "boost/none_t.hpp" |
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| 18 | |
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| 19 | // NOTE: Borland users have to include this header outside any precompiled headers |
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| 20 | // (bcc<=5.64 cannot include instance data in a precompiled header) |
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| 21 | // -- * To be verified, now that there's no unnamed namespace |
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| 22 | |
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| 23 | namespace boost { |
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| 24 | |
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| 25 | #ifdef BOOST_OPTIONAL_USE_OLD_DEFINITION_OF_NONE |
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| 26 | |
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| 27 | BOOST_INLINE_VARIABLE none_t const none = (static_cast<none_t>(0)) ; |
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| 28 | |
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| 29 | #elif defined BOOST_OPTIONAL_USE_SINGLETON_DEFINITION_OF_NONE |
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| 30 | |
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| 31 | namespace detail { namespace optional_detail { |
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| 32 | |
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| 33 | // the trick here is to make boost::none defined once as a global but in a header file |
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| 34 | template <typename T> |
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| 35 | struct none_instance |
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| 36 | { |
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| 37 | static const T instance; |
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| 38 | }; |
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| 39 | |
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| 40 | template <typename T> |
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| 41 | const T none_instance<T>::instance = T(); // global, but because 'tis a template, no cpp file required |
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| 42 | |
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| 43 | } } // namespace detail::optional_detail |
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| 44 | |
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| 45 | |
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| 46 | namespace { |
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| 47 | // TU-local |
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| 48 | const none_t& none = detail::optional_detail::none_instance<none_t>::instance; |
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| 49 | } |
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| 50 | |
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| 51 | #else |
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| 52 | |
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| 53 | BOOST_INLINE_VARIABLE const none_t none ((none_t::init_tag())); |
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| 54 | |
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| 55 | #endif // older definitions |
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| 56 | |
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| 57 | } // namespace boost |
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| 58 | |
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| 59 | #endif // header guard |
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| 60 | |
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| 61 | |
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