1 | // Implementation of std::reference_wrapper -*- C++ -*- |
2 | |
3 | // Copyright (C) 2004-2021 Free Software Foundation, Inc. |
4 | // |
5 | // This file is part of the GNU ISO C++ Library. This library is free |
6 | // software; you can redistribute it and/or modify it under the |
7 | // terms of the GNU General Public License as published by the |
8 | // Free Software Foundation; either version 3, or (at your option) |
9 | // any later version. |
10 | |
11 | // This library is distributed in the hope that it will be useful, |
12 | // but WITHOUT ANY WARRANTY; without even the implied warranty of |
13 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
14 | // GNU General Public License for more details. |
15 | |
16 | // Under Section 7 of GPL version 3, you are granted additional |
17 | // permissions described in the GCC Runtime Library Exception, version |
18 | // 3.1, as published by the Free Software Foundation. |
19 | |
20 | // You should have received a copy of the GNU General Public License and |
21 | // a copy of the GCC Runtime Library Exception along with this program; |
22 | // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
23 | // <http://www.gnu.org/licenses/>. |
24 | |
25 | /** @file include/bits/refwrap.h |
26 | * This is an internal header file, included by other library headers. |
27 | * Do not attempt to use it directly. @headername{functional} |
28 | */ |
29 | |
30 | #ifndef _GLIBCXX_REFWRAP_H |
31 | #define _GLIBCXX_REFWRAP_H 1 |
32 | |
33 | #pragma GCC system_header |
34 | |
35 | #if __cplusplus < 201103L |
36 | # include <bits/c++0x_warning.h> |
37 | #else |
38 | |
39 | #include <bits/move.h> |
40 | #include <bits/invoke.h> |
41 | #include <bits/stl_function.h> // for unary_function and binary_function |
42 | |
43 | namespace std _GLIBCXX_VISIBILITY(default) |
44 | { |
45 | _GLIBCXX_BEGIN_NAMESPACE_VERSION |
46 | |
47 | /// @cond undocumented |
48 | |
49 | /** |
50 | * Derives from @c unary_function or @c binary_function, or perhaps |
51 | * nothing, depending on the number of arguments provided. The |
52 | * primary template is the basis case, which derives nothing. |
53 | */ |
54 | template<typename _Res, typename... _ArgTypes> |
55 | struct _Maybe_unary_or_binary_function { }; |
56 | |
57 | /// Derives from @c unary_function, as appropriate. |
58 | template<typename _Res, typename _T1> |
59 | struct _Maybe_unary_or_binary_function<_Res, _T1> |
60 | : std::unary_function<_T1, _Res> { }; |
61 | |
62 | /// Derives from @c binary_function, as appropriate. |
63 | template<typename _Res, typename _T1, typename _T2> |
64 | struct _Maybe_unary_or_binary_function<_Res, _T1, _T2> |
65 | : std::binary_function<_T1, _T2, _Res> { }; |
66 | |
67 | template<typename _Signature> |
68 | struct _Mem_fn_traits; |
69 | |
70 | template<typename _Res, typename _Class, typename... _ArgTypes> |
71 | struct _Mem_fn_traits_base |
72 | { |
73 | using __result_type = _Res; |
74 | using __maybe_type |
75 | = _Maybe_unary_or_binary_function<_Res, _Class*, _ArgTypes...>; |
76 | using __arity = integral_constant<size_t, sizeof...(_ArgTypes)>; |
77 | }; |
78 | |
79 | #define _GLIBCXX_MEM_FN_TRAITS2(_CV, _REF, _LVAL, _RVAL) \ |
80 | template<typename _Res, typename _Class, typename... _ArgTypes> \ |
81 | struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes...) _CV _REF> \ |
82 | : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \ |
83 | { \ |
84 | using __vararg = false_type; \ |
85 | }; \ |
86 | template<typename _Res, typename _Class, typename... _ArgTypes> \ |
87 | struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes... ...) _CV _REF> \ |
88 | : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \ |
89 | { \ |
90 | using __vararg = true_type; \ |
91 | }; |
92 | |
93 | #define _GLIBCXX_MEM_FN_TRAITS(_REF, _LVAL, _RVAL) \ |
94 | _GLIBCXX_MEM_FN_TRAITS2( , _REF, _LVAL, _RVAL) \ |
95 | _GLIBCXX_MEM_FN_TRAITS2(const , _REF, _LVAL, _RVAL) \ |
96 | _GLIBCXX_MEM_FN_TRAITS2(volatile , _REF, _LVAL, _RVAL) \ |
97 | _GLIBCXX_MEM_FN_TRAITS2(const volatile, _REF, _LVAL, _RVAL) |
98 | |
99 | _GLIBCXX_MEM_FN_TRAITS( , true_type, true_type) |
100 | _GLIBCXX_MEM_FN_TRAITS(&, true_type, false_type) |
101 | _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type) |
102 | |
103 | #if __cplusplus > 201402L |
104 | _GLIBCXX_MEM_FN_TRAITS(noexcept, true_type, true_type) |
105 | _GLIBCXX_MEM_FN_TRAITS(& noexcept, true_type, false_type) |
106 | _GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type) |
107 | #endif |
108 | |
109 | #undef _GLIBCXX_MEM_FN_TRAITS |
110 | #undef _GLIBCXX_MEM_FN_TRAITS2 |
111 | |
112 | /// If we have found a result_type, extract it. |
113 | template<typename _Functor, typename = __void_t<>> |
114 | struct _Maybe_get_result_type |
115 | { }; |
116 | |
117 | template<typename _Functor> |
118 | struct _Maybe_get_result_type<_Functor, |
119 | __void_t<typename _Functor::result_type>> |
120 | { typedef typename _Functor::result_type result_type; }; |
121 | |
122 | /** |
123 | * Base class for any function object that has a weak result type, as |
124 | * defined in 20.8.2 [func.require] of C++11. |
125 | */ |
126 | template<typename _Functor> |
127 | struct _Weak_result_type_impl |
128 | : _Maybe_get_result_type<_Functor> |
129 | { }; |
130 | |
131 | /// Retrieve the result type for a function type. |
132 | template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> |
133 | struct _Weak_result_type_impl<_Res(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL> |
134 | { typedef _Res result_type; }; |
135 | |
136 | /// Retrieve the result type for a varargs function type. |
137 | template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> |
138 | struct _Weak_result_type_impl<_Res(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL> |
139 | { typedef _Res result_type; }; |
140 | |
141 | /// Retrieve the result type for a function pointer. |
142 | template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> |
143 | struct _Weak_result_type_impl<_Res(*)(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL> |
144 | { typedef _Res result_type; }; |
145 | |
146 | /// Retrieve the result type for a varargs function pointer. |
147 | template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> |
148 | struct |
149 | _Weak_result_type_impl<_Res(*)(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL> |
150 | { typedef _Res result_type; }; |
151 | |
152 | // Let _Weak_result_type_impl perform the real work. |
153 | template<typename _Functor, |
154 | bool = is_member_function_pointer<_Functor>::value> |
155 | struct _Weak_result_type_memfun |
156 | : _Weak_result_type_impl<_Functor> |
157 | { }; |
158 | |
159 | // A pointer to member function has a weak result type. |
160 | template<typename _MemFunPtr> |
161 | struct _Weak_result_type_memfun<_MemFunPtr, true> |
162 | { |
163 | using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type; |
164 | }; |
165 | |
166 | // A pointer to data member doesn't have a weak result type. |
167 | template<typename _Func, typename _Class> |
168 | struct _Weak_result_type_memfun<_Func _Class::*, false> |
169 | { }; |
170 | |
171 | /** |
172 | * Strip top-level cv-qualifiers from the function object and let |
173 | * _Weak_result_type_memfun perform the real work. |
174 | */ |
175 | template<typename _Functor> |
176 | struct _Weak_result_type |
177 | : _Weak_result_type_memfun<typename remove_cv<_Functor>::type> |
178 | { }; |
179 | |
180 | #if __cplusplus <= 201703L |
181 | // Detect nested argument_type. |
182 | template<typename _Tp, typename = __void_t<>> |
183 | struct _Refwrap_base_arg1 |
184 | { }; |
185 | |
186 | // Nested argument_type. |
187 | template<typename _Tp> |
188 | struct _Refwrap_base_arg1<_Tp, |
189 | __void_t<typename _Tp::argument_type>> |
190 | { |
191 | typedef typename _Tp::argument_type argument_type; |
192 | }; |
193 | |
194 | // Detect nested first_argument_type and second_argument_type. |
195 | template<typename _Tp, typename = __void_t<>> |
196 | struct _Refwrap_base_arg2 |
197 | { }; |
198 | |
199 | // Nested first_argument_type and second_argument_type. |
200 | template<typename _Tp> |
201 | struct _Refwrap_base_arg2<_Tp, |
202 | __void_t<typename _Tp::first_argument_type, |
203 | typename _Tp::second_argument_type>> |
204 | { |
205 | typedef typename _Tp::first_argument_type first_argument_type; |
206 | typedef typename _Tp::second_argument_type second_argument_type; |
207 | }; |
208 | |
209 | /** |
210 | * Derives from unary_function or binary_function when it |
211 | * can. Specializations handle all of the easy cases. The primary |
212 | * template determines what to do with a class type, which may |
213 | * derive from both unary_function and binary_function. |
214 | */ |
215 | template<typename _Tp> |
216 | struct _Reference_wrapper_base |
217 | : _Weak_result_type<_Tp>, _Refwrap_base_arg1<_Tp>, _Refwrap_base_arg2<_Tp> |
218 | { }; |
219 | |
220 | // - a function type (unary) |
221 | template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM> |
222 | struct _Reference_wrapper_base<_Res(_T1) _GLIBCXX_NOEXCEPT_QUAL> |
223 | : unary_function<_T1, _Res> |
224 | { }; |
225 | |
226 | template<typename _Res, typename _T1> |
227 | struct _Reference_wrapper_base<_Res(_T1) const> |
228 | : unary_function<_T1, _Res> |
229 | { }; |
230 | |
231 | template<typename _Res, typename _T1> |
232 | struct _Reference_wrapper_base<_Res(_T1) volatile> |
233 | : unary_function<_T1, _Res> |
234 | { }; |
235 | |
236 | template<typename _Res, typename _T1> |
237 | struct _Reference_wrapper_base<_Res(_T1) const volatile> |
238 | : unary_function<_T1, _Res> |
239 | { }; |
240 | |
241 | // - a function type (binary) |
242 | template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM> |
243 | struct _Reference_wrapper_base<_Res(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL> |
244 | : binary_function<_T1, _T2, _Res> |
245 | { }; |
246 | |
247 | template<typename _Res, typename _T1, typename _T2> |
248 | struct _Reference_wrapper_base<_Res(_T1, _T2) const> |
249 | : binary_function<_T1, _T2, _Res> |
250 | { }; |
251 | |
252 | template<typename _Res, typename _T1, typename _T2> |
253 | struct _Reference_wrapper_base<_Res(_T1, _T2) volatile> |
254 | : binary_function<_T1, _T2, _Res> |
255 | { }; |
256 | |
257 | template<typename _Res, typename _T1, typename _T2> |
258 | struct _Reference_wrapper_base<_Res(_T1, _T2) const volatile> |
259 | : binary_function<_T1, _T2, _Res> |
260 | { }; |
261 | |
262 | // - a function pointer type (unary) |
263 | template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM> |
264 | struct _Reference_wrapper_base<_Res(*)(_T1) _GLIBCXX_NOEXCEPT_QUAL> |
265 | : unary_function<_T1, _Res> |
266 | { }; |
267 | |
268 | // - a function pointer type (binary) |
269 | template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM> |
270 | struct _Reference_wrapper_base<_Res(*)(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL> |
271 | : binary_function<_T1, _T2, _Res> |
272 | { }; |
273 | |
274 | template<typename _Tp, bool = is_member_function_pointer<_Tp>::value> |
275 | struct _Reference_wrapper_base_memfun |
276 | : _Reference_wrapper_base<_Tp> |
277 | { }; |
278 | |
279 | template<typename _MemFunPtr> |
280 | struct _Reference_wrapper_base_memfun<_MemFunPtr, true> |
281 | : _Mem_fn_traits<_MemFunPtr>::__maybe_type |
282 | { |
283 | using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type; |
284 | }; |
285 | #endif // ! C++20 |
286 | |
287 | /// @endcond |
288 | |
289 | /** |
290 | * @brief Primary class template for reference_wrapper. |
291 | * @ingroup functors |
292 | */ |
293 | template<typename _Tp> |
294 | class reference_wrapper |
295 | #if __cplusplus <= 201703L |
296 | // In C++20 std::reference_wrapper<T> allows T to be incomplete, |
297 | // so checking for nested types could result in ODR violations. |
298 | : public _Reference_wrapper_base_memfun<typename remove_cv<_Tp>::type> |
299 | #endif |
300 | { |
301 | _Tp* _M_data; |
302 | |
303 | _GLIBCXX20_CONSTEXPR |
304 | static _Tp* _S_fun(_Tp& __r) noexcept { return std::__addressof(__r); } |
305 | |
306 | static void _S_fun(_Tp&&) = delete; |
307 | |
308 | template<typename _Up, typename _Up2 = __remove_cvref_t<_Up>> |
309 | using __not_same |
310 | = typename enable_if<!is_same<reference_wrapper, _Up2>::value>::type; |
311 | |
312 | public: |
313 | typedef _Tp type; |
314 | |
315 | // _GLIBCXX_RESOLVE_LIB_DEFECTS |
316 | // 2993. reference_wrapper<T> conversion from T&& |
317 | // 3041. Unnecessary decay in reference_wrapper |
318 | template<typename _Up, typename = __not_same<_Up>, typename |
319 | = decltype(reference_wrapper::_S_fun(std::declval<_Up>()))> |
320 | _GLIBCXX20_CONSTEXPR |
321 | reference_wrapper(_Up&& __uref) |
322 | noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>()))) |
323 | : _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref))) |
324 | { } |
325 | |
326 | reference_wrapper(const reference_wrapper&) = default; |
327 | |
328 | reference_wrapper& |
329 | operator=(const reference_wrapper&) = default; |
330 | |
331 | _GLIBCXX20_CONSTEXPR |
332 | operator _Tp&() const noexcept |
333 | { return this->get(); } |
334 | |
335 | _GLIBCXX20_CONSTEXPR |
336 | _Tp& |
337 | get() const noexcept |
338 | { return *_M_data; } |
339 | |
340 | template<typename... _Args> |
341 | _GLIBCXX20_CONSTEXPR |
342 | typename result_of<_Tp&(_Args&&...)>::type |
343 | operator()(_Args&&... __args) const |
344 | { |
345 | #if __cplusplus > 201703L |
346 | if constexpr (is_object_v<type>) |
347 | static_assert(sizeof(type), "type must be complete" ); |
348 | #endif |
349 | return std::__invoke(get(), std::forward<_Args>(__args)...); |
350 | } |
351 | }; |
352 | |
353 | #if __cpp_deduction_guides |
354 | template<typename _Tp> |
355 | reference_wrapper(_Tp&) -> reference_wrapper<_Tp>; |
356 | #endif |
357 | |
358 | /// @relates reference_wrapper @{ |
359 | |
360 | /// Denotes a reference should be taken to a variable. |
361 | template<typename _Tp> |
362 | _GLIBCXX20_CONSTEXPR |
363 | inline reference_wrapper<_Tp> |
364 | ref(_Tp& __t) noexcept |
365 | { return reference_wrapper<_Tp>(__t); } |
366 | |
367 | /// Denotes a const reference should be taken to a variable. |
368 | template<typename _Tp> |
369 | _GLIBCXX20_CONSTEXPR |
370 | inline reference_wrapper<const _Tp> |
371 | cref(const _Tp& __t) noexcept |
372 | { return reference_wrapper<const _Tp>(__t); } |
373 | |
374 | template<typename _Tp> |
375 | void ref(const _Tp&&) = delete; |
376 | |
377 | template<typename _Tp> |
378 | void cref(const _Tp&&) = delete; |
379 | |
380 | /// std::ref overload to prevent wrapping a reference_wrapper |
381 | template<typename _Tp> |
382 | _GLIBCXX20_CONSTEXPR |
383 | inline reference_wrapper<_Tp> |
384 | ref(reference_wrapper<_Tp> __t) noexcept |
385 | { return __t; } |
386 | |
387 | /// std::cref overload to prevent wrapping a reference_wrapper |
388 | template<typename _Tp> |
389 | _GLIBCXX20_CONSTEXPR |
390 | inline reference_wrapper<const _Tp> |
391 | cref(reference_wrapper<_Tp> __t) noexcept |
392 | { return { __t.get() }; } |
393 | |
394 | /// @} |
395 | |
396 | _GLIBCXX_END_NAMESPACE_VERSION |
397 | } // namespace std |
398 | |
399 | #endif // C++11 |
400 | |
401 | #endif // _GLIBCXX_REFWRAP_H |
402 | |