boost/flyweight/tag.hpp

0001 /* Copyright 2006-2008 Joaquin M Lopez Munoz.
0002  * Distributed under the Boost Software License, Version 1.0.
0003  * (See accompanying file LICENSE_1_0.txt or copy at
0004  * http://www.boost.org/LICENSE_1_0.txt)
0005  *
0006  * See http://www.boost.org/libs/flyweight for library home page.
0007  */
0008
0009 #ifndef BOOST_FLYWEIGHT_TAG_HPP
0010 #define BOOST_FLYWEIGHT_TAG_HPP
0011
0012 #if defined(_MSC_VER)
0013 #pragma once
0014 #endif
0015
0016 #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
0017 #include <boost/parameter/parameters.hpp>
0018 #include <boost/type_traits/is_base_and_derived.hpp>
0019
0020 /* A type T can be used as a tag in the specification of a flyweight
0021  * by passing it wrapped in the form tag<T>.
0022  */
0023
0024 namespace boost{
0025
0026 namespace flyweights{
0027
0028 namespace detail{
0029
0030 struct tag_marker{};
0031
0032 template<typename T>
0033 struct is_tag:is_base_and_derived<tag_marker,T>
0034 {};
0035
0036 } /* namespace flyweights::detail */
0037
0038 template<typename T=parameter::void_>
0039 struct tag:parameter::template_keyword<tag<>,T>,detail::tag_marker
0040 {};
0041
0042 } /* namespace flyweights */
0043
0044 } /* namespace boost */
0045
0046 #endif