ceph/src/boost/libs/optional/include/boost/none.hpp

   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