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 
43namespace 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 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 reference_wrapper(_Up&& __uref) 
316 noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>()))) 
317 : _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref))) 
318 { } 
319 
320 reference_wrapper(const reference_wrapper&) = default; 
321 
322 reference_wrapper& 
323 operator=(const reference_wrapper&) = default; 
324 
325 operator _Tp&() const noexcept 
326 { return this->get(); } 
327 
328 _Tp& 
329 get() const noexcept 
330 { 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 ref(_Tp& __t) noexcept 
353 { 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 
387