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1 : // Implementation of std::reference_wrapper -*- C++ -*-
2 :
3 : // Copyright (C) 2004-2018 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 : // Detect nested argument_type.
179 : template<typename _Tp, typename = __void_t<>>
180 : struct _Refwrap_base_arg1
181 : { };
182 :
183 : // Nested argument_type.
184 : template<typename _Tp>
185 : struct _Refwrap_base_arg1<_Tp,
186 : __void_t<typename _Tp::argument_type>>
187 : {
188 : typedef typename _Tp::argument_type argument_type;
189 : };
190 :
191 : // Detect nested first_argument_type and second_argument_type.
192 : template<typename _Tp, typename = __void_t<>>
193 : struct _Refwrap_base_arg2
194 : { };
195 :
196 : // Nested first_argument_type and second_argument_type.
197 : template<typename _Tp>
198 : struct _Refwrap_base_arg2<_Tp,
199 : __void_t<typename _Tp::first_argument_type,
200 : typename _Tp::second_argument_type>>
201 : {
202 : typedef typename _Tp::first_argument_type first_argument_type;
203 : typedef typename _Tp::second_argument_type second_argument_type;
204 : };
205 :
206 : /**
207 : * Derives from unary_function or binary_function when it
208 : * can. Specializations handle all of the easy cases. The primary
209 : * template determines what to do with a class type, which may
210 : * derive from both unary_function and binary_function.
211 : */
212 : template<typename _Tp>
213 : struct _Reference_wrapper_base
214 : : _Weak_result_type<_Tp>, _Refwrap_base_arg1<_Tp>, _Refwrap_base_arg2<_Tp>
215 : { };
216 :
217 : // - a function type (unary)
218 : template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM>
219 : struct _Reference_wrapper_base<_Res(_T1) _GLIBCXX_NOEXCEPT_QUAL>
220 : : unary_function<_T1, _Res>
221 : { };
222 :
223 : template<typename _Res, typename _T1>
224 : struct _Reference_wrapper_base<_Res(_T1) const>
225 : : unary_function<_T1, _Res>
226 : { };
227 :
228 : template<typename _Res, typename _T1>
229 : struct _Reference_wrapper_base<_Res(_T1) volatile>
230 : : unary_function<_T1, _Res>
231 : { };
232 :
233 : template<typename _Res, typename _T1>
234 : struct _Reference_wrapper_base<_Res(_T1) const volatile>
235 : : unary_function<_T1, _Res>
236 : { };
237 :
238 : // - a function type (binary)
239 : template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM>
240 : struct _Reference_wrapper_base<_Res(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL>
241 : : binary_function<_T1, _T2, _Res>
242 : { };
243 :
244 : template<typename _Res, typename _T1, typename _T2>
245 : struct _Reference_wrapper_base<_Res(_T1, _T2) const>
246 : : binary_function<_T1, _T2, _Res>
247 : { };
248 :
249 : template<typename _Res, typename _T1, typename _T2>
250 : struct _Reference_wrapper_base<_Res(_T1, _T2) volatile>
251 : : binary_function<_T1, _T2, _Res>
252 : { };
253 :
254 : template<typename _Res, typename _T1, typename _T2>
255 : struct _Reference_wrapper_base<_Res(_T1, _T2) const volatile>
256 : : binary_function<_T1, _T2, _Res>
257 : { };
258 :
259 : // - a function pointer type (unary)
260 : template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM>
261 : struct _Reference_wrapper_base<_Res(*)(_T1) _GLIBCXX_NOEXCEPT_QUAL>
262 : : unary_function<_T1, _Res>
263 : { };
264 :
265 : // - a function pointer type (binary)
266 : template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM>
267 : struct _Reference_wrapper_base<_Res(*)(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL>
268 : : binary_function<_T1, _T2, _Res>
269 : { };
270 :
271 : template<typename _Tp, bool = is_member_function_pointer<_Tp>::value>
272 : struct _Reference_wrapper_base_memfun
273 : : _Reference_wrapper_base<_Tp>
274 : { };
275 :
276 : template<typename _MemFunPtr>
277 : struct _Reference_wrapper_base_memfun<_MemFunPtr, true>
278 : : _Mem_fn_traits<_MemFunPtr>::__maybe_type
279 : {
280 : using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type;
281 : };
282 :
283 : /**
284 : * @brief Primary class template for reference_wrapper.
285 : * @ingroup functors
286 : * @{
287 : */
288 : template<typename _Tp>
289 : class reference_wrapper
290 : : public _Reference_wrapper_base_memfun<typename remove_cv<_Tp>::type>
291 : {
292 : _Tp* _M_data;
293 :
294 : public:
295 : typedef _Tp type;
296 :
297 28 : reference_wrapper(_Tp& __indata) noexcept
298 28 : : _M_data(std::__addressof(__indata))
299 28 : { }
300 :
301 : reference_wrapper(_Tp&&) = delete;
302 :
303 : reference_wrapper(const reference_wrapper&) = default;
304 :
305 : reference_wrapper&
306 : operator=(const reference_wrapper&) = default;
307 :
308 : operator _Tp&() const noexcept
309 : { return this->get(); }
310 :
311 : _Tp&
312 56000 : get() const noexcept
313 56000 : { return *_M_data; }
314 :
315 : template<typename... _Args>
316 : typename result_of<_Tp&(_Args&&...)>::type
317 : operator()(_Args&&... __args) const
318 : {
319 : return std::__invoke(get(), std::forward<_Args>(__args)...);
320 : }
321 : };
322 :
323 :
324 : /// Denotes a reference should be taken to a variable.
325 : template<typename _Tp>
326 : inline reference_wrapper<_Tp>
327 : ref(_Tp& __t) noexcept
328 : { return reference_wrapper<_Tp>(__t); }
329 :
330 : /// Denotes a const reference should be taken to a variable.
331 : template<typename _Tp>
332 : inline reference_wrapper<const _Tp>
333 : cref(const _Tp& __t) noexcept
334 : { return reference_wrapper<const _Tp>(__t); }
335 :
336 : template<typename _Tp>
337 : void ref(const _Tp&&) = delete;
338 :
339 : template<typename _Tp>
340 : void cref(const _Tp&&) = delete;
341 :
342 : /// std::ref overload to prevent wrapping a reference_wrapper
343 : template<typename _Tp>
344 : inline reference_wrapper<_Tp>
345 : ref(reference_wrapper<_Tp> __t) noexcept
346 : { return __t; }
347 :
348 : /// std::cref overload to prevent wrapping a reference_wrapper
349 : template<typename _Tp>
350 : inline reference_wrapper<const _Tp>
351 : cref(reference_wrapper<_Tp> __t) noexcept
352 : { return { __t.get() }; }
353 :
354 : // @} group functors
355 :
356 : _GLIBCXX_END_NAMESPACE_VERSION
357 : } // namespace std
358 :
359 : #endif // C++11
360 :
361 : #endif // _GLIBCXX_REFWRAP_H
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