/*=============================================================================
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Copyright (c) 2001-2014 Joel de Guzman
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Copyright (c) 2001-2011 Hartmut Kaiser
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http://spirit.sourceforge.net/
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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=============================================================================*/
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#if !defined(BOOST_SPIRIT_X3_OPTIONAL_TRAITS_FEBRUARY_06_2007_1001AM)
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#define BOOST_SPIRIT_X3_OPTIONAL_TRAITS_FEBRUARY_06_2007_1001AM
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#include <boost/spirit/home/x3/support/unused.hpp>
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#include <boost/optional/optional.hpp>
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#include <boost/mpl/identity.hpp>
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namespace boost { namespace spirit { namespace x3 { namespace traits
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{
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///////////////////////////////////////////////////////////////////////////
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template <typename T, typename Enable = void>
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struct is_optional
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: mpl::false_
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{};
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template <typename T>
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struct is_optional<boost::optional<T>>
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: mpl::true_
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{};
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///////////////////////////////////////////////////////////////////////////
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// build_optional
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//
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// Build a boost::optional from T. Return unused_type if T is unused_type.
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///////////////////////////////////////////////////////////////////////////
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template <typename T>
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struct build_optional
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{
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typedef boost::optional<T> type;
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};
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template <typename T>
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struct build_optional<boost::optional<T> >
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{
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typedef boost::optional<T> type;
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};
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template <>
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struct build_optional<unused_type>
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{
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typedef unused_type type;
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};
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///////////////////////////////////////////////////////////////////////////
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// optional_value
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//
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// Get the optional's value_type. Handles unused_type as well.
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///////////////////////////////////////////////////////////////////////////
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template <typename T>
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struct optional_value : mpl::identity<T> {};
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template <typename T>
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struct optional_value<boost::optional<T> >
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: mpl::identity<T> {};
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template <>
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struct optional_value<unused_type>
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: mpl::identity<unused_type> {};
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template <>
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struct optional_value<unused_type const>
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: mpl::identity<unused_type> {};
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}}}}
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#endif
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