boost/flyweight/holder_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_HOLDER_TAG_HPP
0010 #define BOOST_FLYWEIGHT_HOLDER_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 namespace boost{
0021
0022 namespace flyweights{
0023
0024 /* Three ways to indicate that a given class T is a holder specifier:
0025  *   1. Make it derived from holder_marker.
0026  *   2. Specialize is_holder to evaluate to boost::mpl::true_.
0027  *   3. Pass it as holder<T> when defining a flyweight type.
0028  */
0029
0030 struct holder_marker{};
0031
0032 template<typename T>
0033 struct is_holder:is_base_and_derived<holder_marker,T>
0034 {};
0035
0036 template<typename T=parameter::void_>
0037 struct holder:parameter::template_keyword<holder<>,T>
0038 {};
0039
0040 } /* namespace flyweights */
0041
0042 } /* namespace boost */
0043
0044 #endif