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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_FACTORY_TAG_HPP
+#define BOOST_FLYWEIGHT_FACTORY_TAG_HPP
+
+#if defined(_MSC_VER)&&(_MSC_VER>=1200)
+#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{
+
+/* Three ways to indicate that a given class T is a factory specifier:
+ * 1. Make it derived from factory_marker.
+ * 2. Specialize is_factory to evaluate to boost::mpl::true_.
+ * 3. Pass it as factory<T> when defining a flyweight type.
+ */
+
+struct factory_marker{};
+
+template<typename T>
+struct is_factory:is_base_and_derived<factory_marker,T>
+{};
+
+template<typename T=parameter::void_>
+struct factory:parameter::template_keyword<factory<>,T>
+{};
+
+} /* namespace flyweights */
+
+} /* namespace boost */
+
+#endif