51 lines
1.2 KiB
C++
51 lines
1.2 KiB
C++
/* Copyright 2006-2008 Joaquin M Lopez Munoz.
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* Distributed under the Boost Software License, Version 1.0.
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* (See accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* See http://www.boost.org/libs/flyweight for library home page.
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*/
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#ifndef BOOST_FLYWEIGHT_DETAIL_VALUE_TAG_HPP
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#define BOOST_FLYWEIGHT_DETAIL_VALUE_TAG_HPP
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#if defined(_MSC_VER)&&(_MSC_VER>=1200)
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#pragma once
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#endif
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#include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
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#include <boost/parameter/parameters.hpp>
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#include <boost/type_traits/is_base_and_derived.hpp>
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namespace boost{
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namespace flyweights{
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namespace detail{
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/* Three ways to indicate that a given class T is a value policy:
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* 1. Make it derived from value_marker.
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* 2. Specialize is_value to evaluate to boost::mpl::true_.
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* 3. Pass it as value<T> when defining a flyweight type.
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*
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* For the time being the interface of value policies is not public.
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*/
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struct value_marker{};
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template<typename T>
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struct is_value:is_base_and_derived<value_marker,T>
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{};
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template<typename T=parameter::void_>
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struct value:parameter::template_keyword<value<>,T>
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{};
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} /* namespace flyweights::detail */
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} /* namespace flyweights */
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} /* namespace boost */
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#endif
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