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Editing: recursive_variant.hpp
//----------------------------------------------------------------------------- // boost variant/recursive_variant.hpp header file // See http://www.boost.org for updates, documentation, and revision history. //----------------------------------------------------------------------------- // // Copyright (c) 2003 Eric Friedman // Copyright (c) 2013-2020 Antony Polukhin // // 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) #ifndef BOOST_VARIANT_RECURSIVE_VARIANT_HPP #define BOOST_VARIANT_RECURSIVE_VARIANT_HPP #include <boost/variant/variant_fwd.hpp> #include <boost/variant/detail/enable_recursive.hpp> #include <boost/variant/detail/substitute_fwd.hpp> #include <boost/variant/detail/make_variant_list.hpp> #include <boost/variant/detail/over_sequence.hpp> #include <boost/mpl/aux_/lambda_arity_param.hpp> #include <boost/mpl/equal.hpp> #include <boost/mpl/eval_if.hpp> #include <boost/mpl/identity.hpp> #include <boost/mpl/if.hpp> #include <boost/mpl/protect.hpp> #include <boost/mpl/transform.hpp> #include <boost/type_traits/is_same.hpp> #include <boost/preprocessor/cat.hpp> #include <boost/preprocessor/repeat.hpp> #include <boost/mpl/bool.hpp> #include <boost/mpl/is_sequence.hpp> #include <boost/variant/variant.hpp> namespace boost { namespace detail { namespace variant { /////////////////////////////////////////////////////////////////////////////// // (detail) metafunction specialization substitute // // Handles embedded variant types when substituting for recursive_variant_. // #if !defined(BOOST_VARIANT_DETAIL_NO_SUBSTITUTE) template < BOOST_VARIANT_ENUM_PARAMS(typename T) , typename RecursiveVariant BOOST_MPL_AUX_LAMBDA_ARITY_PARAM(typename Arity) > struct substitute< ::boost::variant< recursive_flag< T0 > , BOOST_VARIANT_ENUM_SHIFTED_PARAMS(T) > , RecursiveVariant , ::boost::recursive_variant_ BOOST_MPL_AUX_LAMBDA_ARITY_PARAM(Arity) > { typedef ::boost::variant< recursive_flag< T0 > , BOOST_VARIANT_ENUM_SHIFTED_PARAMS(T) > type; }; template < BOOST_VARIANT_ENUM_PARAMS(typename T) , typename RecursiveVariant BOOST_MPL_AUX_LAMBDA_ARITY_PARAM(typename Arity) > struct substitute< ::boost::variant< ::boost::detail::variant::over_sequence< T0 > , BOOST_VARIANT_ENUM_SHIFTED_PARAMS(T) > , RecursiveVariant , ::boost::recursive_variant_ BOOST_MPL_AUX_LAMBDA_ARITY_PARAM(Arity) > { private: typedef T0 initial_types; typedef typename mpl::transform< initial_types , mpl::protect< quoted_enable_recursive<RecursiveVariant,mpl::true_> > >::type types; public: typedef typename mpl::if_< mpl::equal<initial_types, types, ::boost::is_same<mpl::_1, mpl::_2> > , ::boost::variant< ::boost::detail::variant::over_sequence< T0 > , BOOST_VARIANT_ENUM_SHIFTED_PARAMS(T) > , ::boost::variant< over_sequence<types> > >::type type; }; template < BOOST_VARIANT_ENUM_PARAMS(typename T) , typename RecursiveVariant BOOST_MPL_AUX_LAMBDA_ARITY_PARAM(typename Arity) > struct substitute< ::boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) > , RecursiveVariant , ::boost::recursive_variant_ BOOST_MPL_AUX_LAMBDA_ARITY_PARAM(Arity) > { #if !defined(BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES) typedef ::boost::variant< typename enable_recursive< T0 , RecursiveVariant , mpl::true_ >::type, typename enable_recursive< TN , RecursiveVariant , mpl::true_ >::type... > type; #else // defined(BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES) private: // helpers, for metafunction result (below) #define BOOST_VARIANT_AUX_ENABLE_RECURSIVE_TYPEDEFS(z,N,_) \ typedef typename enable_recursive< \ BOOST_PP_CAT(T,N) \ , RecursiveVariant \ , mpl::true_ \ >::type BOOST_PP_CAT(wknd_T,N); \ /**/ BOOST_PP_REPEAT( BOOST_VARIANT_LIMIT_TYPES , BOOST_VARIANT_AUX_ENABLE_RECURSIVE_TYPEDEFS , _ ) #undef BOOST_VARIANT_AUX_ENABLE_RECURSIVE_TYPEDEFS public: // metafunction result typedef ::boost::variant< BOOST_VARIANT_ENUM_PARAMS(wknd_T) > type; #endif // BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES workaround }; #else // defined(BOOST_VARIANT_DETAIL_NO_SUBSTITUTE) // // no specializations: embedded variants unsupported on these compilers! // #endif // !defined(BOOST_VARIANT_DETAIL_NO_SUBSTITUTE) }} // namespace detail::variant /////////////////////////////////////////////////////////////////////////////// // metafunction make_recursive_variant // // See docs and boost/variant/variant_fwd.hpp for more information. // template < BOOST_VARIANT_ENUM_PARAMS(typename T) > struct make_recursive_variant { public: // metafunction result typedef boost::variant< detail::variant::recursive_flag< T0 > , BOOST_VARIANT_ENUM_SHIFTED_PARAMS(T) > type; }; /////////////////////////////////////////////////////////////////////////////// // metafunction make_recursive_variant_over // // See docs and boost/variant/variant_fwd.hpp for more information. // template <typename Types> struct make_recursive_variant_over { private: // precondition assertions BOOST_STATIC_ASSERT(( ::boost::mpl::is_sequence<Types>::value )); public: // metafunction result typedef typename make_recursive_variant< detail::variant::over_sequence< Types > >::type type; }; } // namespace boost #endif // BOOST_VARIANT_RECURSIVE_VARIANT_HPP
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