support/traits/is_variant.hpp

0001 /*=============================================================================
0002     Copyright (c) 2001-2014 Joel de Guzman
0003     http://spirit.sourceforge.net/
0004
0005     Distributed under the Boost Software License, Version 1.0. (See accompanying
0006     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0007 =============================================================================*/
0008 #if !defined(BOOST_SPIRIT_X3_IS_VARIANT_JAN_10_2012_0823AM)
0009 #define BOOST_SPIRIT_X3_IS_VARIANT_JAN_10_2012_0823AM
0010
0011 #include <boost/variant.hpp>
0012 #include <boost/mpl/has_xxx.hpp>
0013 #include <boost/mpl/bool.hpp>
0014
0015 namespace boost { namespace spirit { namespace x3 { namespace traits
0016 {
0017     namespace detail
0018     {
0019         // By declaring a nested struct in your class/struct, you tell
0020         // spirit that it is regarded as a variant type. The minimum
0021         // required interface for such a variant is that it has constructors
0022         // for various types supported by your variant and a typedef 'types'
0023         // which is an mpl sequence of the contained types.
0024         //
0025         // This is an intrusive interface. For a non-intrusive interface,
0026         // use the is_variant trait.
0027         BOOST_MPL_HAS_XXX_TRAIT_DEF(adapted_variant_tag)
0028     }
0029
0030     template <typename T, typename Enable = void>
0031     struct is_variant
0032       : detail::has_adapted_variant_tag<T>
0033     {};
0034
0035     template <BOOST_VARIANT_ENUM_PARAMS(typename T)>
0036     struct is_variant<boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>>
0037       : mpl::true_
0038     {};
0039 }}}}
0040
0041 #endif