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 60