boost/flyweight/tag.hpp

/* 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_TAG_HPP
#define BOOST_FLYWEIGHT_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>
/* A type T can be used as a tag in the specification of a flyweight
 * by passing it wrapped in the form tag<T>.
 */
namespace boost{
namespace flyweights{
namespace detail{
struct tag_marker{};
template<typename T>
struct is_tag:is_base_and_derived<tag_marker,T>
{};
} /* namespace flyweights::detail */
template<typename T=parameter::void_>
struct tag:parameter::template_keyword<tag<>,T>,detail::tag_marker
{};
} /* namespace flyweights */
} /* namespace boost */
#endif