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
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 // 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 reference_wrapper(_Tp& __indata) noexcept
298 : _M_data(std::__addressof(__indata))
299 { }
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 get() const noexcept
313 { 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
362