1//-----------------------------------------------------------------------------
2// boost variant/variant_fwd.hpp header file
3// See http://www.boost.org for updates, documentation, and revision history.
4//-----------------------------------------------------------------------------
5//
6// Copyright (c) 2003 Eric Friedman, Itay Maman
7// Copyright (c) 2013-2023 Antony Polukhin
8//
9// Distributed under the Boost Software License, Version 1.0. (See
10// accompanying file LICENSE_1_0.txt or copy at
11// http://www.boost.org/LICENSE_1_0.txt)
12
13#ifndef BOOST_VARIANT_VARIANT_FWD_HPP
14#define BOOST_VARIANT_VARIANT_FWD_HPP
15
16#include <boost/variant/detail/config.hpp>
17
18#include <boost/blank_fwd.hpp>
19#include <boost/mpl/arg.hpp>
20#include <boost/mpl/limits/arity.hpp>
21#include <boost/mpl/aux_/na.hpp>
22#include <boost/preprocessor/cat.hpp>
23#include <boost/preprocessor/enum.hpp>
24#include <boost/preprocessor/enum_params.hpp>
25#include <boost/preprocessor/enum_shifted_params.hpp>
26#include <boost/preprocessor/repeat.hpp>
27
28///////////////////////////////////////////////////////////////////////////////
29// macro BOOST_VARIANT_NO_TYPE_SEQUENCE_SUPPORT
30//
31// Defined if variant does not support make_variant_over (see below).
32//
33#if defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE)
34# define BOOST_VARIANT_NO_TYPE_SEQUENCE_SUPPORT
35#endif
36
37///////////////////////////////////////////////////////////////////////////////
38// macro BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT
39//
40// Defined if make_recursive_variant cannot be supported as documented.
41//
42// Note: Currently, MPL lambda facility is used as workaround if defined, and
43// so only types declared w/ MPL lambda workarounds will work.
44//
45
46#include <boost/variant/detail/substitute_fwd.hpp>
47
48#if defined(BOOST_VARIANT_DETAIL_NO_SUBSTITUTE) \
49 && !defined(BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT)
50# define BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT
51#endif
52
53
54///////////////////////////////////////////////////////////////////////////////
55// macro BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES
56//
57
58/*
59 GCC before 4.0 had no variadic tempaltes;
60 GCC 4.6 has incomplete implementation of variadic templates.
61
62 MSVC2015 Update 1 has variadic templates, but they have issues.
63
64 NOTE: Clang compiler defines __GNUC__
65*/
66#if defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) \
67 || (!defined(__clang__) && defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ < 7)) \
68 || (defined(_MSC_VER) && (_MSC_VER <= 1900)) \
69 || defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE) \
70 || defined (BOOST_VARIANT_NO_TYPE_SEQUENCE_SUPPORT)
71
72#ifndef BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES
73# define BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES
74#endif
75
76#endif
77
78#if !defined(BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES)
79#include <boost/preprocessor/seq/size.hpp>
80
81#define BOOST_VARIANT_CLASS_OR_TYPENAME_TO_SEQ_class class)(
82#define BOOST_VARIANT_CLASS_OR_TYPENAME_TO_SEQ_typename typename)(
83
84#define BOOST_VARIANT_CLASS_OR_TYPENAME_TO_VARIADIC_class class...
85#define BOOST_VARIANT_CLASS_OR_TYPENAME_TO_VARIADIC_typename typename...
86
87#define ARGS_VARIADER_1(x) x ## N...
88#define ARGS_VARIADER_2(x) BOOST_VARIANT_CLASS_OR_TYPENAME_TO_VARIADIC_ ## x ## N
89
90#define BOOST_VARIANT_MAKE_VARIADIC(sequence, x) BOOST_VARIANT_MAKE_VARIADIC_I(BOOST_PP_SEQ_SIZE(sequence), x)
91#define BOOST_VARIANT_MAKE_VARIADIC_I(argscount, x) BOOST_VARIANT_MAKE_VARIADIC_II(argscount, x)
92#define BOOST_VARIANT_MAKE_VARIADIC_II(argscount, orig) ARGS_VARIADER_ ## argscount(orig)
93
94///////////////////////////////////////////////////////////////////////////////
95// BOOST_VARIANT_ENUM_PARAMS and BOOST_VARIANT_ENUM_SHIFTED_PARAMS
96//
97// Convenience macro for enumeration of variant params.
98// When variadic templates are available expands:
99// BOOST_VARIANT_ENUM_PARAMS(class Something) => class Something0, class... SomethingN
100// BOOST_VARIANT_ENUM_PARAMS(typename Something) => typename Something0, typename... SomethingN
101// BOOST_VARIANT_ENUM_PARAMS(Something) => Something0, SomethingN...
102// BOOST_VARIANT_ENUM_PARAMS(Something) => Something0, SomethingN...
103// BOOST_VARIANT_ENUM_SHIFTED_PARAMS(class Something) => class... SomethingN
104// BOOST_VARIANT_ENUM_SHIFTED_PARAMS(typename Something) => typename... SomethingN
105// BOOST_VARIANT_ENUM_SHIFTED_PARAMS(Something) => SomethingN...
106// BOOST_VARIANT_ENUM_SHIFTED_PARAMS(Something) => SomethingN...
107//
108// Rationale: Cleaner, simpler code for clients of variant library. Minimal
109// code modifications to move from C++03 to C++11.
110//
111// With BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES defined
112// will be used BOOST_VARIANT_ENUM_PARAMS and BOOST_VARIANT_ENUM_SHIFTED_PARAMS from below `#else`
113//
114
115#define BOOST_VARIANT_ENUM_PARAMS(x) \
116 x ## 0, \
117 BOOST_VARIANT_MAKE_VARIADIC( (BOOST_VARIANT_CLASS_OR_TYPENAME_TO_SEQ_ ## x), x) \
118 /**/
119
120#define BOOST_VARIANT_ENUM_SHIFTED_PARAMS(x) \
121 BOOST_VARIANT_MAKE_VARIADIC( (BOOST_VARIANT_CLASS_OR_TYPENAME_TO_SEQ_ ## x), x) \
122 /**/
123
124#else // defined(BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES)
125
126///////////////////////////////////////////////////////////////////////////////
127// macro BOOST_VARIANT_LIMIT_TYPES
128//
129// Implementation-defined preprocessor symbol describing the actual
130// length of variant's pseudo-variadic template parameter list.
131//
132#include <boost/mpl/limits/list.hpp>
133#define BOOST_VARIANT_LIMIT_TYPES \
134 BOOST_MPL_LIMIT_LIST_SIZE
135
136///////////////////////////////////////////////////////////////////////////////
137// macro BOOST_VARIANT_RECURSIVE_VARIANT_MAX_ARITY
138//
139// Exposes maximum allowed arity of class templates with recursive_variant
140// arguments. That is,
141// make_recursive_variant< ..., T<[1], recursive_variant_, ... [N]> >.
142//
143#include <boost/mpl/limits/arity.hpp>
144#define BOOST_VARIANT_RECURSIVE_VARIANT_MAX_ARITY \
145 BOOST_MPL_LIMIT_METAFUNCTION_ARITY
146
147///////////////////////////////////////////////////////////////////////////////
148// macro BOOST_VARIANT_ENUM_PARAMS
149//
150// Convenience macro for enumeration of BOOST_VARIANT_LIMIT_TYPES params.
151//
152// Rationale: Cleaner, simpler code for clients of variant library.
153//
154#define BOOST_VARIANT_ENUM_PARAMS( param ) \
155 BOOST_PP_ENUM_PARAMS(BOOST_VARIANT_LIMIT_TYPES, param)
156
157///////////////////////////////////////////////////////////////////////////////
158// macro BOOST_VARIANT_ENUM_SHIFTED_PARAMS
159//
160// Convenience macro for enumeration of BOOST_VARIANT_LIMIT_TYPES-1 params.
161//
162#define BOOST_VARIANT_ENUM_SHIFTED_PARAMS( param ) \
163 BOOST_PP_ENUM_SHIFTED_PARAMS(BOOST_VARIANT_LIMIT_TYPES, param)
164
165#endif // BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES workaround
166
167
168namespace boost {
169
170namespace detail { namespace variant {
171
172///////////////////////////////////////////////////////////////////////////////
173// (detail) class void_ and class template convert_void
174//
175// Provides the mechanism by which void(NN) types are converted to
176// mpl::void_ (and thus can be passed to mpl::list).
177//
178// Rationale: This is particularly needed for the using-declarations
179// workaround (below), but also to avoid associating mpl namespace with
180// variant in argument dependent lookups (which used to happen because of
181// defaulting of template parameters to mpl::void_).
182//
183
184struct void_;
185
186template <typename T>
187struct convert_void
188{
189 typedef T type;
190};
191
192template <>
193struct convert_void< void_ >
194{
195 typedef mpl::na type;
196};
197
198///////////////////////////////////////////////////////////////////////////////
199// (workaround) BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE
200//
201// Needed to work around compilers that don't support using-declaration
202// overloads. (See the variant::initializer workarounds below.)
203//
204
205#if defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE)
206// (detail) tags voidNN -- NN defined on [0, BOOST_VARIANT_LIMIT_TYPES)
207//
208// Defines void types that are each unique and specializations of
209// convert_void that yields mpl::na for each voidNN type.
210//
211
212#define BOOST_VARIANT_DETAIL_DEFINE_VOID_N(z,N,_) \
213 struct BOOST_PP_CAT(void,N); \
214 \
215 template <> \
216 struct convert_void< BOOST_PP_CAT(void,N) > \
217 { \
218 typedef mpl::na type; \
219 }; \
220 /**/
221
222BOOST_PP_REPEAT(
223 BOOST_VARIANT_LIMIT_TYPES
224 , BOOST_VARIANT_DETAIL_DEFINE_VOID_N
225 , _
226 )
227
228#undef BOOST_VARIANT_DETAIL_DEFINE_VOID_N
229
230#endif // BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE workaround
231
232}} // namespace detail::variant
233
234#if !defined(BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES)
235# define BOOST_VARIANT_AUX_DECLARE_PARAMS BOOST_VARIANT_ENUM_PARAMS(typename T)
236#else // defined(BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES)
237
238///////////////////////////////////////////////////////////////////////////////
239// (detail) macro BOOST_VARIANT_AUX_DECLARE_PARAM
240//
241// Template parameter list for variant and recursive_variant declarations.
242//
243
244#if !defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE)
245
246# define BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL(z, N, T) \
247 typename BOOST_PP_CAT(T,N) = detail::variant::void_ \
248 /**/
249
250#else // defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE)
251
252# define BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL(z, N, T) \
253 typename BOOST_PP_CAT(T,N) = BOOST_PP_CAT(detail::variant::void,N) \
254 /**/
255
256#endif // BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE workaround
257
258#define BOOST_VARIANT_AUX_DECLARE_PARAMS \
259 BOOST_PP_ENUM( \
260 BOOST_VARIANT_LIMIT_TYPES \
261 , BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL \
262 , T \
263 ) \
264 /**/
265
266#endif // BOOST_VARIANT_DO_NOT_USE_VARIADIC_TEMPLATES workaround
267
268///////////////////////////////////////////////////////////////////////////////
269// class template variant (concept inspired by Andrei Alexandrescu)
270//
271// Efficient, type-safe bounded discriminated union.
272//
273// Preconditions:
274// - Each type must be unique.
275// - No type may be const-qualified.
276//
277// Proper declaration form:
278// variant<types> (where types is a type-sequence)
279// or
280// variant<T0,T1,...,Tn> (where T0 is NOT a type-sequence)
281//
282template < BOOST_VARIANT_AUX_DECLARE_PARAMS > class variant;
283
284///////////////////////////////////////////////////////////////////////////////
285// metafunction make_recursive_variant
286//
287// Exposes a boost::variant with recursive_variant_ tags (below) substituted
288// with the variant itself (wrapped as needed with boost::recursive_wrapper).
289//
290template < BOOST_VARIANT_AUX_DECLARE_PARAMS > struct make_recursive_variant;
291
292#undef BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL
293#undef BOOST_VARIANT_AUX_DECLARE_PARAMS
294
295///////////////////////////////////////////////////////////////////////////////
296// type recursive_variant_
297//
298// Tag type indicates where recursive variant substitution should occur.
299//
300#if !defined(BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT)
301 struct recursive_variant_ {};
302#else
303 typedef mpl::arg<1> recursive_variant_;
304#endif
305
306///////////////////////////////////////////////////////////////////////////////
307// metafunction make_variant_over
308//
309// Result is a variant w/ types of the specified type sequence.
310//
311template <typename Types> struct make_variant_over;
312
313///////////////////////////////////////////////////////////////////////////////
314// metafunction make_recursive_variant_over
315//
316// Result is a recursive variant w/ types of the specified type sequence.
317//
318template <typename Types> struct make_recursive_variant_over;
319
320} // namespace boost
321
322#endif // BOOST_VARIANT_VARIANT_FWD_HPP
323