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0001 //----------------------------------------------------------------------------- 0002 // boost variant/variant_fwd.hpp header file 0003 // See http://www.boost.org for updates, documentation, and revision history. 0004 //----------------------------------------------------------------------------- 0005 // 0006 // Copyright (c) 2003 Eric Friedman, Itay Maman 0007 // Copyright (c) 2013-2025 Antony Polukhin 0008 // 0009 // Distributed under the Boost Software License, Version 1.0. (See 0010 // accompanying file LICENSE_1_0.txt or copy at 0011 // http://www.boost.org/LICENSE_1_0.txt) 0012 0013 #ifndef BOOST_VARIANT_VARIANT_FWD_HPP 0014 #define BOOST_VARIANT_VARIANT_FWD_HPP 0015 0016 #include <boost/variant/detail/config.hpp> 0017 0018 #include <boost/blank_fwd.hpp> 0019 #include <boost/mpl/arg.hpp> 0020 #include <boost/mpl/limits/arity.hpp> 0021 #include <boost/mpl/aux_/na.hpp> 0022 #include <boost/preprocessor/cat.hpp> 0023 #include <boost/preprocessor/enum.hpp> 0024 #include <boost/preprocessor/enum_params.hpp> 0025 #include <boost/preprocessor/enum_shifted_params.hpp> 0026 #include <boost/preprocessor/repeat.hpp> 0027 0028 /////////////////////////////////////////////////////////////////////////////// 0029 // macro BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT 0030 // 0031 // Defined if make_recursive_variant cannot be supported as documented. 0032 // 0033 // Note: Currently, MPL lambda facility is used as workaround if defined, and 0034 // so only types declared w/ MPL lambda workarounds will work. 0035 // 0036 0037 #include <boost/variant/detail/substitute_fwd.hpp> 0038 0039 #include <boost/preprocessor/seq/size.hpp> 0040 0041 #define BOOST_VARIANT_CLASS_OR_TYPENAME_TO_SEQ_class class)( 0042 #define BOOST_VARIANT_CLASS_OR_TYPENAME_TO_SEQ_typename typename)( 0043 0044 #define BOOST_VARIANT_CLASS_OR_TYPENAME_TO_VARIADIC_class class... 0045 #define BOOST_VARIANT_CLASS_OR_TYPENAME_TO_VARIADIC_typename typename... 0046 0047 #define ARGS_VARIADER_1(x) x ## N... 0048 #define ARGS_VARIADER_2(x) BOOST_VARIANT_CLASS_OR_TYPENAME_TO_VARIADIC_ ## x ## N 0049 0050 #define BOOST_VARIANT_MAKE_VARIADIC(sequence, x) BOOST_VARIANT_MAKE_VARIADIC_I(BOOST_PP_SEQ_SIZE(sequence), x) 0051 #define BOOST_VARIANT_MAKE_VARIADIC_I(argscount, x) BOOST_VARIANT_MAKE_VARIADIC_II(argscount, x) 0052 #define BOOST_VARIANT_MAKE_VARIADIC_II(argscount, orig) ARGS_VARIADER_ ## argscount(orig) 0053 0054 /////////////////////////////////////////////////////////////////////////////// 0055 // BOOST_VARIANT_ENUM_PARAMS and BOOST_VARIANT_ENUM_SHIFTED_PARAMS 0056 // 0057 // Convenience macro for enumeration of variant params. 0058 // When variadic templates are available expands: 0059 // BOOST_VARIANT_ENUM_PARAMS(class Something) => class Something0, class... SomethingN 0060 // BOOST_VARIANT_ENUM_PARAMS(typename Something) => typename Something0, typename... SomethingN 0061 // BOOST_VARIANT_ENUM_PARAMS(Something) => Something0, SomethingN... 0062 // BOOST_VARIANT_ENUM_PARAMS(Something) => Something0, SomethingN... 0063 // BOOST_VARIANT_ENUM_SHIFTED_PARAMS(class Something) => class... SomethingN 0064 // BOOST_VARIANT_ENUM_SHIFTED_PARAMS(typename Something) => typename... SomethingN 0065 // BOOST_VARIANT_ENUM_SHIFTED_PARAMS(Something) => SomethingN... 0066 // BOOST_VARIANT_ENUM_SHIFTED_PARAMS(Something) => SomethingN... 0067 // 0068 // Rationale: Cleaner, simpler code for clients of variant library. Minimal 0069 // code modifications to move from C++03 to C++11. 0070 // 0071 0072 #define BOOST_VARIANT_ENUM_PARAMS(x) \ 0073 x ## 0, \ 0074 BOOST_VARIANT_MAKE_VARIADIC( (BOOST_VARIANT_CLASS_OR_TYPENAME_TO_SEQ_ ## x), x) \ 0075 /**/ 0076 0077 #define BOOST_VARIANT_ENUM_SHIFTED_PARAMS(x) \ 0078 BOOST_VARIANT_MAKE_VARIADIC( (BOOST_VARIANT_CLASS_OR_TYPENAME_TO_SEQ_ ## x), x) \ 0079 /**/ 0080 0081 0082 namespace boost { 0083 0084 namespace detail { namespace variant { 0085 0086 /////////////////////////////////////////////////////////////////////////////// 0087 // (detail) class void_ and class template convert_void 0088 // 0089 // Provides the mechanism by which void(NN) types are converted to 0090 // mpl::void_ (and thus can be passed to mpl::list). 0091 // 0092 // Rationale: This is particularly needed for the using-declarations 0093 // workaround (below), but also to avoid associating mpl namespace with 0094 // variant in argument dependent lookups (which used to happen because of 0095 // defaulting of template parameters to mpl::void_). 0096 // 0097 0098 struct void_; 0099 0100 template <typename T> 0101 struct convert_void 0102 { 0103 typedef T type; 0104 }; 0105 0106 template <> 0107 struct convert_void< void_ > 0108 { 0109 typedef mpl::na type; 0110 }; 0111 0112 }} // namespace detail::variant 0113 0114 #define BOOST_VARIANT_AUX_DECLARE_PARAMS BOOST_VARIANT_ENUM_PARAMS(typename T) 0115 0116 /////////////////////////////////////////////////////////////////////////////// 0117 // class template variant (concept inspired by Andrei Alexandrescu) 0118 // 0119 // Efficient, type-safe bounded discriminated union. 0120 // 0121 // Preconditions: 0122 // - Each type must be unique. 0123 // - No type may be const-qualified. 0124 // 0125 // Proper declaration form: 0126 // variant<types> (where types is a type-sequence) 0127 // or 0128 // variant<T0,T1,...,Tn> (where T0 is NOT a type-sequence) 0129 // 0130 template < BOOST_VARIANT_AUX_DECLARE_PARAMS > class variant; 0131 0132 /////////////////////////////////////////////////////////////////////////////// 0133 // metafunction make_recursive_variant 0134 // 0135 // Exposes a boost::variant with recursive_variant_ tags (below) substituted 0136 // with the variant itself (wrapped as needed with boost::recursive_wrapper). 0137 // 0138 template < BOOST_VARIANT_AUX_DECLARE_PARAMS > struct make_recursive_variant; 0139 0140 #undef BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL 0141 #undef BOOST_VARIANT_AUX_DECLARE_PARAMS 0142 0143 /////////////////////////////////////////////////////////////////////////////// 0144 // type recursive_variant_ 0145 // 0146 // Tag type indicates where recursive variant substitution should occur. 0147 // 0148 #if !defined(BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT) 0149 struct recursive_variant_ {}; 0150 #else 0151 typedef mpl::arg<1> recursive_variant_; 0152 #endif 0153 0154 /////////////////////////////////////////////////////////////////////////////// 0155 // metafunction make_variant_over 0156 // 0157 // Result is a variant w/ types of the specified type sequence. 0158 // 0159 template <typename Types> struct make_variant_over; 0160 0161 /////////////////////////////////////////////////////////////////////////////// 0162 // metafunction make_recursive_variant_over 0163 // 0164 // Result is a recursive variant w/ types of the specified type sequence. 0165 // 0166 template <typename Types> struct make_recursive_variant_over; 0167 0168 } // namespace boost 0169 0170 #endif // BOOST_VARIANT_VARIANT_FWD_HPP
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