// Boost.TypeErasure library
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//
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// Copyright 2011 Steven Watanabe
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//
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// Distributed under the Boost Software License Version 1.0. (See
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// 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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// $Id$
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#ifndef BOOST_TYPE_ERASURE_DEDUCED_HPP_INCLUDED
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#define BOOST_TYPE_ERASURE_DEDUCED_HPP_INCLUDED
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#include <boost/mpl/eval_if.hpp>
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#include <boost/mpl/identity.hpp>
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#include <boost/mpl/set.hpp>
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#include <boost/mpl/empty.hpp>
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#include <boost/type_erasure/detail/get_placeholders.hpp>
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#include <boost/type_erasure/placeholder.hpp>
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namespace boost {
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namespace type_erasure {
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/**
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* A placeholder for an associated type. The type corresponding
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* to this placeholder is deduced by substituting placeholders
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* in the arguments of the metafunction and then evaluating it.
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*
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* When using @ref deduced in a template context, if it is possible for
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* Metafunction to contain no placeholders at all, use the nested type,
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* to automatically evaluate it early as needed.
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*/
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template<class Metafunction>
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struct deduced : ::boost::type_erasure::placeholder
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{
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typedef typename ::boost::mpl::eval_if<
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::boost::mpl::empty<
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typename ::boost::type_erasure::detail::get_placeholders<
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Metafunction,
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#ifndef BOOST_TYPE_ERASURE_USE_MP11
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::boost::mpl::set0<>
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#else
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::boost::mp11::mp_list<>
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#endif
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>::type
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>,
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Metafunction,
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::boost::mpl::identity<
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::boost::type_erasure::deduced<Metafunction>
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>
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>::type type;
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};
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}
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}
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#endif
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