ceph/src/boost/boost/flyweight/detail/value_tag.hpp

   1 /* Copyright 2006-2008 Joaquin M Lopez Munoz.
   2  * Distributed under the Boost Software License, Version 1.0.
   3  * (See accompanying file LICENSE_1_0.txt or copy at
   4  * http://www.boost.org/LICENSE_1_0.txt)
   5  *
   6  * See http://www.boost.org/libs/flyweight for library home page.
   7  */
   8
   9 #ifndef BOOST_FLYWEIGHT_DETAIL_VALUE_TAG_HPP
  10 #define BOOST_FLYWEIGHT_DETAIL_VALUE_TAG_HPP
  11
  12 #if defined(_MSC_VER)
  13 #pragma once
  14 #endif
  15
  16 #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
  17 #include <boost/parameter/parameters.hpp>
  18 #include <boost/type_traits/is_base_and_derived.hpp>
  19
  20 namespace boost{
  21
  22 namespace flyweights{
  23
  24 namespace detail{
  25
  26 /* Three ways to indicate that a given class T is a value policy:
  27  *   1. Make it derived from value_marker.
  28  *   2. Specialize is_value to evaluate to boost::mpl::true_.
  29  *   3. Pass it as value<T> when defining a flyweight type.
  30  *
  31  * For the time being the interface of value policies is not public.
  32  */
  33
  34 struct value_marker{};
  35
  36 template<typename T>
  37 struct is_value:is_base_and_derived<value_marker,T>
  38 {};
  39
  40 template<typename T=parameter::void_>
  41 struct value:parameter::template_keyword<value<>,T>
  42 {};
  43
  44 } /* namespace flyweights::detail */
  45
  46 } /* namespace flyweights */
  47
  48 } /* namespace boost */
  49
  50 #endif