1 // Implementation of std::reference_wrapper -*- C++ -*- 2 3 // Copyright (C) 2004-2022 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 37 #include <bits/move.h> 38 #include <bits/invoke.h> 39 #include <bits/stl_function.h> // for unary_function and binary_function 40 41 namespace std _GLIBCXX_VISIBILITY(default) 42 { 43 _GLIBCXX_BEGIN_NAMESPACE_VERSION 44 45 /// @cond undocumented 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 // Ignore warnings about unary_function and binary_function. 56 #pragma GCC diagnostic push 57 #pragma GCC diagnostic ignored "-Wdeprecated-declarations" 58 59 /// Derives from @c unary_function, as appropriate. 60 template<typename _Res, typename _T1> 61 struct _Maybe_unary_or_binary_function<_Res, _T1> 62 : std::unary_function<_T1, _Res> { }; 63 64 /// Derives from @c binary_function, as appropriate. 65 template<typename _Res, typename _T1, typename _T2> 66 struct _Maybe_unary_or_binary_function<_Res, _T1, _T2> 67 : std::binary_function<_T1, _T2, _Res> { }; 68 69 #pragma GCC diagnostic pop 70 71 template<typename _Signature> 72 struct _Mem_fn_traits; 73 74 template<typename _Res, typename _Class, typename... _ArgTypes> 75 struct _Mem_fn_traits_base 76 { 77 using __result_type = _Res; 78 using __maybe_type 79 = _Maybe_unary_or_binary_function<_Res, _Class*, _ArgTypes...>; 80 using __arity = integral_constant<size_t, sizeof...(_ArgTypes)>; 81 }; 82 83 #define _GLIBCXX_MEM_FN_TRAITS2(_CV, _REF, _LVAL, _RVAL) \ 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 = false_type; \ 89 }; \ 90 template<typename _Res, typename _Class, typename... _ArgTypes> \ 91 struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes... ...) _CV _REF> \ 92 : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \ 93 { \ 94 using __vararg = true_type; \ 95 }; 96 97 #define _GLIBCXX_MEM_FN_TRAITS(_REF, _LVAL, _RVAL) \ 98 _GLIBCXX_MEM_FN_TRAITS2( , _REF, _LVAL, _RVAL) \ 99 _GLIBCXX_MEM_FN_TRAITS2(const , _REF, _LVAL, _RVAL) \ 100 _GLIBCXX_MEM_FN_TRAITS2(volatile , _REF, _LVAL, _RVAL) \ 101 _GLIBCXX_MEM_FN_TRAITS2(const volatile, _REF, _LVAL, _RVAL) 102 103 _GLIBCXX_MEM_FN_TRAITS( , true_type, true_type) 104 _GLIBCXX_MEM_FN_TRAITS(&, true_type, false_type) 105 _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type) 106 107 #if __cplusplus > 201402L 108 _GLIBCXX_MEM_FN_TRAITS(noexcept, true_type, true_type) 109 _GLIBCXX_MEM_FN_TRAITS(& noexcept, true_type, false_type) 110 _GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type) 111 #endif 112 113 #undef _GLIBCXX_MEM_FN_TRAITS 114 #undef _GLIBCXX_MEM_FN_TRAITS2 115 116 /// If we have found a result_type, extract it. 117 template<typename _Functor, typename = __void_t<>> 118 struct _Maybe_get_result_type 119 { }; 120 121 template<typename _Functor> 122 struct _Maybe_get_result_type<_Functor, 123 __void_t<typename _Functor::result_type>> 124 { typedef typename _Functor::result_type result_type; }; 125 126 /** 127 * Base class for any function object that has a weak result type, as 128 * defined in 20.8.2 [func.require] of C++11. 129 */ 130 template<typename _Functor> 131 struct _Weak_result_type_impl 132 : _Maybe_get_result_type<_Functor> 133 { }; 134 135 /// Retrieve the result type for a function type. 136 template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> 137 struct _Weak_result_type_impl<_Res(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL> 138 { typedef _Res result_type; }; 139 140 /// Retrieve the result type for a varargs function type. 141 template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> 142 struct _Weak_result_type_impl<_Res(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL> 143 { typedef _Res result_type; }; 144 145 /// Retrieve the result type for a function pointer. 146 template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> 147 struct _Weak_result_type_impl<_Res(*)(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL> 148 { typedef _Res result_type; }; 149 150 /// Retrieve the result type for a varargs function pointer. 151 template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> 152 struct 153 _Weak_result_type_impl<_Res(*)(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL> 154 { typedef _Res result_type; }; 155 156 // Let _Weak_result_type_impl perform the real work. 157 template<typename _Functor, 158 bool = is_member_function_pointer<_Functor>::value> 159 struct _Weak_result_type_memfun 160 : _Weak_result_type_impl<_Functor> 161 { }; 162 163 // A pointer to member function has a weak result type. 164 template<typename _MemFunPtr> 165 struct _Weak_result_type_memfun<_MemFunPtr, true> 166 { 167 using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type; 168 }; 169 170 // A pointer to data member doesn't have a weak result type. 171 template<typename _Func, typename _Class> 172 struct _Weak_result_type_memfun<_Func _Class::*, false> 173 { }; 174 175 /** 176 * Strip top-level cv-qualifiers from the function object and let 177 * _Weak_result_type_memfun perform the real work. 178 */ 179 template<typename _Functor> 180 struct _Weak_result_type 181 : _Weak_result_type_memfun<typename remove_cv<_Functor>::type> 182 { }; 183 184 #if __cplusplus <= 201703L 185 // Detect nested argument_type. 186 template<typename _Tp, typename = __void_t<>> 187 struct _Refwrap_base_arg1 188 { }; 189 190 // Nested argument_type. 191 template<typename _Tp> 192 struct _Refwrap_base_arg1<_Tp, 193 __void_t<typename _Tp::argument_type>> 194 { 195 typedef typename _Tp::argument_type argument_type; 196 }; 197 198 // Detect nested first_argument_type and second_argument_type. 199 template<typename _Tp, typename = __void_t<>> 200 struct _Refwrap_base_arg2 201 { }; 202 203 // Nested first_argument_type and second_argument_type. 204 template<typename _Tp> 205 struct _Refwrap_base_arg2<_Tp, 206 __void_t<typename _Tp::first_argument_type, 207 typename _Tp::second_argument_type>> 208 { 209 typedef typename _Tp::first_argument_type first_argument_type; 210 typedef typename _Tp::second_argument_type second_argument_type; 211 }; 212 213 /** 214 * Derives from unary_function or binary_function when it 215 * can. Specializations handle all of the easy cases. The primary 216 * template determines what to do with a class type, which may 217 * derive from both unary_function and binary_function. 218 */ 219 template<typename _Tp> 220 struct _Reference_wrapper_base 221 : _Weak_result_type<_Tp>, _Refwrap_base_arg1<_Tp>, _Refwrap_base_arg2<_Tp> 222 { }; 223 224 // Ignore warnings about unary_function and binary_function. 225 #pragma GCC diagnostic push 226 #pragma GCC diagnostic ignored "-Wdeprecated-declarations" 227 228 // - a function type (unary) 229 template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM> 230 struct _Reference_wrapper_base<_Res(_T1) _GLIBCXX_NOEXCEPT_QUAL> 231 : unary_function<_T1, _Res> 232 { }; 233 234 template<typename _Res, typename _T1> 235 struct _Reference_wrapper_base<_Res(_T1) const> 236 : unary_function<_T1, _Res> 237 { }; 238 239 template<typename _Res, typename _T1> 240 struct _Reference_wrapper_base<_Res(_T1) volatile> 241 : unary_function<_T1, _Res> 242 { }; 243 244 template<typename _Res, typename _T1> 245 struct _Reference_wrapper_base<_Res(_T1) const volatile> 246 : unary_function<_T1, _Res> 247 { }; 248 249 // - a function type (binary) 250 template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM> 251 struct _Reference_wrapper_base<_Res(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL> 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> 257 : binary_function<_T1, _T2, _Res> 258 { }; 259 260 template<typename _Res, typename _T1, typename _T2> 261 struct _Reference_wrapper_base<_Res(_T1, _T2) volatile> 262 : binary_function<_T1, _T2, _Res> 263 { }; 264 265 template<typename _Res, typename _T1, typename _T2> 266 struct _Reference_wrapper_base<_Res(_T1, _T2) const volatile> 267 : binary_function<_T1, _T2, _Res> 268 { }; 269 270 // - a function pointer type (unary) 271 template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM> 272 struct _Reference_wrapper_base<_Res(*)(_T1) _GLIBCXX_NOEXCEPT_QUAL> 273 : unary_function<_T1, _Res> 274 { }; 275 276 // - a function pointer type (binary) 277 template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM> 278 struct _Reference_wrapper_base<_Res(*)(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL> 279 : binary_function<_T1, _T2, _Res> 280 { }; 281 282 template<typename _Tp, bool = is_member_function_pointer<_Tp>::value> 283 struct _Reference_wrapper_base_memfun 284 : _Reference_wrapper_base<_Tp> 285 { }; 286 287 template<typename _MemFunPtr> 288 struct _Reference_wrapper_base_memfun<_MemFunPtr, true> 289 : _Mem_fn_traits<_MemFunPtr>::__maybe_type 290 { 291 using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type; 292 }; 293 #pragma GCC diagnostic pop 294 #endif // ! C++20 295 296 /// @endcond 297 298 /** 299 * @brief Primary class template for reference_wrapper. 300 * @ingroup functors 301 */ 302 template<typename _Tp> 303 class reference_wrapper 304 #if __cplusplus <= 201703L 305 // In C++20 std::reference_wrapper<T> allows T to be incomplete, 306 // so checking for nested types could result in ODR violations. 307 : public _Reference_wrapper_base_memfun<typename remove_cv<_Tp>::type> 308 #endif 309 { 310 _Tp* _M_data; 311 312 _GLIBCXX20_CONSTEXPR 313 static _Tp* _S_fun(_Tp& __r) noexcept { return std::__addressof(__r); } 314 315 static void _S_fun(_Tp&&) = delete; 316 317 template<typename _Up, typename _Up2 = __remove_cvref_t<_Up>> 318 using __not_same 319 = typename enable_if<!is_same<reference_wrapper, _Up2>::value>::type; 320 321 public: 322 typedef _Tp type; 323 324 // _GLIBCXX_RESOLVE_LIB_DEFECTS 325 // 2993. reference_wrapper<T> conversion from T&& 326 // 3041. Unnecessary decay in reference_wrapper 327 template<typename _Up, typename = __not_same<_Up>, typename 328 = decltype(reference_wrapper::_S_fun(std::declval<_Up>()))> 329 _GLIBCXX20_CONSTEXPR 330 reference_wrapper(_Up&& __uref) 331 noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>()))) 332 : _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref))) 333 { } 334 335 reference_wrapper(const reference_wrapper&) = default; 336 337 reference_wrapper& 338 operator=(const reference_wrapper&) = default; 339 340 _GLIBCXX20_CONSTEXPR 341 operator _Tp&() const noexcept 342 { return this->get(); } 343 344 _GLIBCXX20_CONSTEXPR 345 _Tp& 346 get() const noexcept 347 { return *_M_data; } 348 349 template<typename... _Args> 350 _GLIBCXX20_CONSTEXPR 351 typename __invoke_result<_Tp&, _Args...>::type 352 operator()(_Args&&... __args) const 353 noexcept(__is_nothrow_invocable<_Tp&, _Args...>::value) 354 { 355 #if __cplusplus > 201703L 356 if constexpr (is_object_v<type>) 357 static_assert(sizeof(type), "type must be complete"); 358 #endif 359 return std::__invoke(get(), std::forward<_Args>(__args)...); 360 } 361 }; 362 363 #if __cpp_deduction_guides 364 template<typename _Tp> 365 reference_wrapper(_Tp&) -> reference_wrapper<_Tp>; 366 #endif 367 368 /// @relates reference_wrapper @{ 369 370 /// Denotes a reference should be taken to a variable. 371 template<typename _Tp> 372 _GLIBCXX20_CONSTEXPR 373 inline reference_wrapper<_Tp> 374 ref(_Tp& __t) noexcept 375 { return reference_wrapper<_Tp>(__t); } 376 377 /// Denotes a const reference should be taken to a variable. 378 template<typename _Tp> 379 _GLIBCXX20_CONSTEXPR 380 inline reference_wrapper<const _Tp> 381 cref(const _Tp& __t) noexcept 382 { return reference_wrapper<const _Tp>(__t); } 383 384 template<typename _Tp> 385 void ref(const _Tp&&) = delete; 386 387 template<typename _Tp> 388 void cref(const _Tp&&) = delete; 389 390 /// std::ref overload to prevent wrapping a reference_wrapper 391 template<typename _Tp> 392 _GLIBCXX20_CONSTEXPR 393 inline reference_wrapper<_Tp> 394 ref(reference_wrapper<_Tp> __t) noexcept 395 { return __t; } 396 397 /// std::cref overload to prevent wrapping a reference_wrapper 398 template<typename _Tp> 399 _GLIBCXX20_CONSTEXPR 400 inline reference_wrapper<const _Tp> 401 cref(reference_wrapper<_Tp> __t) noexcept 402 { return { __t.get() }; } 403 404 /// @} 405 406 _GLIBCXX_END_NAMESPACE_VERSION 407 } // namespace std 408 409 #endif // C++11 410 411 #endif // _GLIBCXX_REFWRAP_H 412
Indexes created Tue Feb 24 08:35:24 UTC 2026