boost/flyweight/holder_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_HOLDER_TAG_HPP #define BOOST_FLYWEIGHT_HOLDER_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 holder specifier: * 1. Make it derived from holder_marker. * 2. Specialize is_holder to evaluate to boost::mpl::true_. * 3. Pass it as holder<T> when defining a flyweight type. */ struct holder_marker{}; template<typename T> struct is_holder:is_base_and_derived<holder_marker,T> {}; template<typename T=parameter::void_> struct holder:parameter::template_keyword<holder<>,T> {}; } /* namespace flyweights */ } /* namespace boost */ #endif