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1 : // Implementation of std::reference_wrapper -*- C++ -*-
2 :
3 : // Copyright (C) 2004-2019 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 : /**
48 : * Derives from @c unary_function or @c binary_function, or perhaps
49 : * nothing, depending on the number of arguments provided. The
50 : * primary template is the basis case, which derives nothing.
51 : */
52 : template<typename _Res, typename... _ArgTypes>
53 : struct _Maybe_unary_or_binary_function { };
54 :
55 : /// Derives from @c unary_function, as appropriate.
56 : template<typename _Res, typename _T1>
57 : struct _Maybe_unary_or_binary_function<_Res, _T1>
58 : : std::unary_function<_T1, _Res> { };
59 :
60 : /// Derives from @c binary_function, as appropriate.
61 : template<typename _Res, typename _T1, typename _T2>
62 : struct _Maybe_unary_or_binary_function<_Res, _T1, _T2>
63 : : std::binary_function<_T1, _T2, _Res> { };
64 :
65 : template<typename _Signature>
66 : struct _Mem_fn_traits;
67 :
68 : template<typename _Res, typename _Class, typename... _ArgTypes>
69 : struct _Mem_fn_traits_base
70 : {
71 : using __result_type = _Res;
72 : using __maybe_type
73 : = _Maybe_unary_or_binary_function<_Res, _Class*, _ArgTypes...>;
74 : using __arity = integral_constant<size_t, sizeof...(_ArgTypes)>;
75 : };
76 :
77 : #define _GLIBCXX_MEM_FN_TRAITS2(_CV, _REF, _LVAL, _RVAL) \
78 : template<typename _Res, typename _Class, typename... _ArgTypes> \
79 : struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes...) _CV _REF> \
80 : : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \
81 : { \
82 : using __vararg = false_type; \
83 : }; \
84 : template<typename _Res, typename _Class, typename... _ArgTypes> \
85 : struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes... ...) _CV _REF> \
86 : : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \
87 : { \
88 : using __vararg = true_type; \
89 : };
90 :
91 : #define _GLIBCXX_MEM_FN_TRAITS(_REF, _LVAL, _RVAL) \
92 : _GLIBCXX_MEM_FN_TRAITS2( , _REF, _LVAL, _RVAL) \
93 : _GLIBCXX_MEM_FN_TRAITS2(const , _REF, _LVAL, _RVAL) \
94 : _GLIBCXX_MEM_FN_TRAITS2(volatile , _REF, _LVAL, _RVAL) \
95 : _GLIBCXX_MEM_FN_TRAITS2(const volatile, _REF, _LVAL, _RVAL)
96 :
97 : _GLIBCXX_MEM_FN_TRAITS( , true_type, true_type)
98 : _GLIBCXX_MEM_FN_TRAITS(&, true_type, false_type)
99 : _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type)
100 :
101 : #if __cplusplus > 201402L
102 : _GLIBCXX_MEM_FN_TRAITS(noexcept, true_type, true_type)
103 : _GLIBCXX_MEM_FN_TRAITS(& noexcept, true_type, false_type)
104 : _GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type)
105 : #endif
106 :
107 : #undef _GLIBCXX_MEM_FN_TRAITS
108 : #undef _GLIBCXX_MEM_FN_TRAITS2
109 :
110 : /// If we have found a result_type, extract it.
111 : template<typename _Functor, typename = __void_t<>>
112 : struct _Maybe_get_result_type
113 : { };
114 :
115 : template<typename _Functor>
116 : struct _Maybe_get_result_type<_Functor,
117 : __void_t<typename _Functor::result_type>>
118 : { typedef typename _Functor::result_type result_type; };
119 :
120 : /**
121 : * Base class for any function object that has a weak result type, as
122 : * defined in 20.8.2 [func.require] of C++11.
123 : */
124 : template<typename _Functor>
125 : struct _Weak_result_type_impl
126 : : _Maybe_get_result_type<_Functor>
127 : { };
128 :
129 : /// Retrieve the result type for a function type.
130 : template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
131 : struct _Weak_result_type_impl<_Res(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL>
132 : { typedef _Res result_type; };
133 :
134 : /// Retrieve the result type for a varargs function type.
135 : template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
136 : struct _Weak_result_type_impl<_Res(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL>
137 : { typedef _Res result_type; };
138 :
139 : /// Retrieve the result type for a function pointer.
140 : template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
141 : struct _Weak_result_type_impl<_Res(*)(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL>
142 : { typedef _Res result_type; };
143 :
144 : /// Retrieve the result type for a varargs function pointer.
145 : template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM>
146 : struct
147 : _Weak_result_type_impl<_Res(*)(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL>
148 : { typedef _Res result_type; };
149 :
150 : // Let _Weak_result_type_impl perform the real work.
151 : template<typename _Functor,
152 : bool = is_member_function_pointer<_Functor>::value>
153 : struct _Weak_result_type_memfun
154 : : _Weak_result_type_impl<_Functor>
155 : { };
156 :
157 : // A pointer to member function has a weak result type.
158 : template<typename _MemFunPtr>
159 : struct _Weak_result_type_memfun<_MemFunPtr, true>
160 : {
161 : using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type;
162 : };
163 :
164 : // A pointer to data member doesn't have a weak result type.
165 : template<typename _Func, typename _Class>
166 : struct _Weak_result_type_memfun<_Func _Class::*, false>
167 : { };
168 :
169 : /**
170 : * Strip top-level cv-qualifiers from the function object and let
171 : * _Weak_result_type_memfun perform the real work.
172 : */
173 : template<typename _Functor>
174 : struct _Weak_result_type
175 : : _Weak_result_type_memfun<typename remove_cv<_Functor>::type>
176 : { };
177 :
178 : #if __cplusplus <= 201703L
179 : // Detect nested argument_type.
180 : template<typename _Tp, typename = __void_t<>>
181 : struct _Refwrap_base_arg1
182 : { };
183 :
184 : // Nested argument_type.
185 : template<typename _Tp>
186 : struct _Refwrap_base_arg1<_Tp,
187 : __void_t<typename _Tp::argument_type>>
188 : {
189 : typedef typename _Tp::argument_type argument_type;
190 : };
191 :
192 : // Detect nested first_argument_type and second_argument_type.
193 : template<typename _Tp, typename = __void_t<>>
194 : struct _Refwrap_base_arg2
195 : { };
196 :
197 : // Nested first_argument_type and second_argument_type.
198 : template<typename _Tp>
199 : struct _Refwrap_base_arg2<_Tp,
200 : __void_t<typename _Tp::first_argument_type,
201 : typename _Tp::second_argument_type>>
202 : {
203 : typedef typename _Tp::first_argument_type first_argument_type;
204 : typedef typename _Tp::second_argument_type second_argument_type;
205 : };
206 :
207 : /**
208 : * Derives from unary_function or binary_function when it
209 : * can. Specializations handle all of the easy cases. The primary
210 : * template determines what to do with a class type, which may
211 : * derive from both unary_function and binary_function.
212 : */
213 : template<typename _Tp>
214 : struct _Reference_wrapper_base
215 : : _Weak_result_type<_Tp>, _Refwrap_base_arg1<_Tp>, _Refwrap_base_arg2<_Tp>
216 : { };
217 :
218 : // - a function type (unary)
219 : template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM>
220 : struct _Reference_wrapper_base<_Res(_T1) _GLIBCXX_NOEXCEPT_QUAL>
221 : : unary_function<_T1, _Res>
222 : { };
223 :
224 : template<typename _Res, typename _T1>
225 : struct _Reference_wrapper_base<_Res(_T1) const>
226 : : unary_function<_T1, _Res>
227 : { };
228 :
229 : template<typename _Res, typename _T1>
230 : struct _Reference_wrapper_base<_Res(_T1) volatile>
231 : : unary_function<_T1, _Res>
232 : { };
233 :
234 : template<typename _Res, typename _T1>
235 : struct _Reference_wrapper_base<_Res(_T1) const volatile>
236 : : unary_function<_T1, _Res>
237 : { };
238 :
239 : // - a function type (binary)
240 : template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM>
241 : struct _Reference_wrapper_base<_Res(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL>
242 : : binary_function<_T1, _T2, _Res>
243 : { };
244 :
245 : template<typename _Res, typename _T1, typename _T2>
246 : struct _Reference_wrapper_base<_Res(_T1, _T2) const>
247 : : binary_function<_T1, _T2, _Res>
248 : { };
249 :
250 : template<typename _Res, typename _T1, typename _T2>
251 : struct _Reference_wrapper_base<_Res(_T1, _T2) volatile>
252 : : binary_function<_T1, _T2, _Res>
253 : { };
254 :
255 : template<typename _Res, typename _T1, typename _T2>
256 : struct _Reference_wrapper_base<_Res(_T1, _T2) const volatile>
257 : : binary_function<_T1, _T2, _Res>
258 : { };
259 :
260 : // - a function pointer type (unary)
261 : template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM>
262 : struct _Reference_wrapper_base<_Res(*)(_T1) _GLIBCXX_NOEXCEPT_QUAL>
263 : : unary_function<_T1, _Res>
264 : { };
265 :
266 : // - a function pointer type (binary)
267 : template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM>
268 : struct _Reference_wrapper_base<_Res(*)(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL>
269 : : binary_function<_T1, _T2, _Res>
270 : { };
271 :
272 : template<typename _Tp, bool = is_member_function_pointer<_Tp>::value>
273 : struct _Reference_wrapper_base_memfun
274 : : _Reference_wrapper_base<_Tp>
275 : { };
276 :
277 : template<typename _MemFunPtr>
278 : struct _Reference_wrapper_base_memfun<_MemFunPtr, true>
279 : : _Mem_fn_traits<_MemFunPtr>::__maybe_type
280 : {
281 : using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type;
282 : };
283 : #endif // ! C++20
284 :
285 : /**
286 : * @brief Primary class template for reference_wrapper.
287 : * @ingroup functors
288 : * @{
289 : */
290 : template<typename _Tp>
291 : class reference_wrapper
292 : #if __cplusplus <= 201703L
293 : // In C++20 std::reference_wrapper<T> allows T to be incomplete,
294 : // so checking for nested types could result in ODR violations.
295 : : public _Reference_wrapper_base_memfun<typename remove_cv<_Tp>::type>
296 : #endif
297 : {
298 : _Tp* _M_data;
299 :
300 0 : static _Tp* _S_fun(_Tp& __r) noexcept { return std::__addressof(__r); }
301 : static void _S_fun(_Tp&&) = delete;
302 :
303 : template<typename _Up, typename _Up2 = __remove_cvref_t<_Up>>
304 : using __not_same
305 : = typename enable_if<!is_same<reference_wrapper, _Up2>::value>::type;
306 :
307 : public:
308 : typedef _Tp type;
309 :
310 : // _GLIBCXX_RESOLVE_LIB_DEFECTS
311 : // 2993. reference_wrapper<T> conversion from T&&
312 : // 3041. Unnecessary decay in reference_wrapper
313 : template<typename _Up, typename = __not_same<_Up>, typename
314 : = decltype(reference_wrapper::_S_fun(std::declval<_Up>()))>
315 0 : reference_wrapper(_Up&& __uref)
316 : noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>())))
317 0 : : _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref)))
318 0 : { }
319 :
320 : reference_wrapper(const reference_wrapper&) = default;
321 :
322 : reference_wrapper&
323 : operator=(const reference_wrapper&) = default;
324 :
325 0 : operator _Tp&() const noexcept
326 0 : { return this->get(); }
327 :
328 : _Tp&
329 0 : get() const noexcept
330 0 : { return *_M_data; }
331 :
332 : template<typename... _Args>
333 : typename result_of<_Tp&(_Args&&...)>::type
334 : operator()(_Args&&... __args) const
335 : {
336 : #if __cplusplus > 201703L
337 : if constexpr (is_object_v<type>)
338 : static_assert(sizeof(type), "type must be complete");
339 : #endif
340 : return std::__invoke(get(), std::forward<_Args>(__args)...);
341 : }
342 : };
343 :
344 : #if __cpp_deduction_guides
345 : template<typename _Tp>
346 : reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
347 : #endif
348 :
349 : /// Denotes a reference should be taken to a variable.
350 : template<typename _Tp>
351 : inline reference_wrapper<_Tp>
352 0 : ref(_Tp& __t) noexcept
353 0 : { return reference_wrapper<_Tp>(__t); }
354 :
355 : /// Denotes a const reference should be taken to a variable.
356 : template<typename _Tp>
357 : inline reference_wrapper<const _Tp>
358 : cref(const _Tp& __t) noexcept
359 : { return reference_wrapper<const _Tp>(__t); }
360 :
361 : template<typename _Tp>
362 : void ref(const _Tp&&) = delete;
363 :
364 : template<typename _Tp>
365 : void cref(const _Tp&&) = delete;
366 :
367 : /// std::ref overload to prevent wrapping a reference_wrapper
368 : template<typename _Tp>
369 : inline reference_wrapper<_Tp>
370 : ref(reference_wrapper<_Tp> __t) noexcept
371 : { return __t; }
372 :
373 : /// std::cref overload to prevent wrapping a reference_wrapper
374 : template<typename _Tp>
375 : inline reference_wrapper<const _Tp>
376 : cref(reference_wrapper<_Tp> __t) noexcept
377 : { return { __t.get() }; }
378 :
379 : /// @} group functors
380 :
381 : _GLIBCXX_END_NAMESPACE_VERSION
382 : } // namespace std
383 :
384 : #endif // C++11
385 :
386 : #endif // _GLIBCXX_REFWRAP_H
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