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