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/* Copyright 2006-2008 Joaquin M Lopez Munoz.
* 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/flyweight for library home page.
*/
#ifndef BOOST_FLYWEIGHT_DETAIL_VALUE_TAG_HPP
#define BOOST_FLYWEIGHT_DETAIL_VALUE_TAG_HPP
#if defined(_MSC_VER)
#pragma once
#endif
#include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
#include <boost/parameter/parameters.hpp>
#include <boost/type_traits/is_base_and_derived.hpp>
namespace boost{
namespace flyweights{
namespace detail{
/* Three ways to indicate that a given class T is a value policy:
* 1. Make it derived from value_marker.
* 2. Specialize is_value to evaluate to boost::mpl::true_.
* 3. Pass it as value<T> when defining a flyweight type.
*
* For the time being the interface of value policies is not public.
*/
struct value_marker{};
template<typename T>
struct is_value:is_base_and_derived<value_marker,T>
{};
template<typename T=parameter::void_>
struct value:parameter::template_keyword<value<>,T>
{};
} /* namespace flyweights::detail */
} /* namespace flyweights */
} /* namespace boost */
#endif
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