598bfd3f
 Hu Chunming
提交_GLIBCXX_USE_CX...
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// Copyright (C) 2003, Fernando Luis Cacciola Carballal.
// Copyright (C) 2014, 2015 Andrzej Krzemienski.
//
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/libs/optional for documentation.
//
// You are welcome to contact the author at:
// fernando_cacciola@hotmail.com
//
#ifndef BOOST_NONE_17SEP2003_HPP
#define BOOST_NONE_17SEP2003_HPP
#include "boost/config.hpp"
#include "boost/none_t.hpp"
// NOTE: Borland users have to include this header outside any precompiled headers
// (bcc<=5.64 cannot include instance data in a precompiled header)
// -- * To be verified, now that there's no unnamed namespace
namespace boost {
#ifdef BOOST_OPTIONAL_USE_OLD_DEFINITION_OF_NONE
BOOST_INLINE_VARIABLE none_t BOOST_CONSTEXPR_OR_CONST none = (static_cast<none_t>(0)) ;
#elif defined BOOST_OPTIONAL_USE_SINGLETON_DEFINITION_OF_NONE
namespace detail { namespace optional_detail {
// the trick here is to make boost::none defined once as a global but in a header file
template <typename T>
struct none_instance
{
static const T instance;
};
template <typename T>
const T none_instance<T>::instance = T(); // global, but because 'tis a template, no cpp file required
} } // namespace detail::optional_detail
namespace {
// TU-local
const none_t& none = detail::optional_detail::none_instance<none_t>::instance;
}
#else
BOOST_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST none_t none ((none_t::init_tag()));
#endif // older definitions
} // namespace boost
#endif // header guard
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