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
20namespace boost{
21
22namespace flyweights{
23
24namespace 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
34struct value_marker{};
35
36template<typename T>
37struct is_value:is_base_and_derived<value_marker,T>
38{};
39
40template<typename T=parameter::void_>
41struct value:parameter::template_keyword<value<>,T>
42{};
43
44} /* namespace flyweights::detail */
45
46} /* namespace flyweights */
47
48} /* namespace boost */
49
50#endif
51

source code of boost/libs/flyweight/include/boost/flyweight/detail/value_tag.hpp