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)
6 * See http://www.boost.org/libs/flyweight for library home page.
9 #ifndef BOOST_FLYWEIGHT_HOLDER_TAG_HPP
10 #define BOOST_FLYWEIGHT_HOLDER_TAG_HPP
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>
24 /* Three ways to indicate that a given class T is a holder specifier:
25 * 1. Make it derived from holder_marker.
26 * 2. Specialize is_holder to evaluate to boost::mpl::true_.
27 * 3. Pass it as holder<T> when defining a flyweight type.
30 struct holder_marker{};
33 struct is_holder:is_base_and_derived<holder_marker,T>
36 template<typename T=parameter::void_>
37 struct holder:parameter::template_keyword<holder<>,T>
40 } /* namespace flyweights */
42 } /* namespace boost */