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https://github.com/boostorg/optional.git
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60 lines
1.6 KiB
C++
60 lines
1.6 KiB
C++
// Copyright (C) 2003, Fernando Luis Cacciola Carballal.
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// Copyright (C) 2014, 2015 Andrzej Krzemienski.
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//
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// See http://www.boost.org/libs/optional for documentation.
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//
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// You are welcome to contact the author at:
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// fernando_cacciola@hotmail.com
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//
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#ifndef BOOST_NONE_17SEP2003_HPP
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#define BOOST_NONE_17SEP2003_HPP
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#include "boost/config.hpp"
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#include "boost/none_t.hpp"
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// NOTE: Borland users have to include this header outside any precompiled headers
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// (bcc<=5.64 cannot include instance data in a precompiled header)
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// -- * To be verified, now that there's no unnamed namespace
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namespace boost {
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#ifdef BOOST_OPTIONAL_USE_OLD_DEFINITION_OF_NONE
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BOOST_INLINE_VARIABLE none_t BOOST_CONSTEXPR_OR_CONST none = (static_cast<none_t>(0)) ;
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#elif defined BOOST_OPTIONAL_USE_SINGLETON_DEFINITION_OF_NONE
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namespace detail { namespace optional_detail {
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// the trick here is to make boost::none defined once as a global but in a header file
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template <typename T>
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struct none_instance
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{
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static const T instance;
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};
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template <typename T>
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const T none_instance<T>::instance = T(); // global, but because 'tis a template, no cpp file required
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} } // namespace detail::optional_detail
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namespace {
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// TU-local
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const none_t& none = detail::optional_detail::none_instance<none_t>::instance;
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}
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#else
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BOOST_INLINE_CONSTEXPR none_t none ((none_t::init_tag()));
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#endif // older definitions
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} // namespace boost
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#endif // header guard
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