/*=============================================================================
    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
