60 lines
1.6 KiB
C++
60 lines
1.6 KiB
C++
|
// 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/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
|
||
|
|
|
||
|
|
none_t 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
|
||
|
|
|
||
|
|
const none_t none ((none_t::init_tag()));
|
||
|
|
|
||
|
|
#endif // older definitions
|
||
|
|
|
||
|
|
} // namespace boost
|
||
|
|
|
||
|
|
#endif // header guard
|
||
|
|
|