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The C and C++ Include Header Files
cat -n /usr/include/c++/15/bits/refwrap.h
1 // Implementation of std::reference_wrapper -*- C++ -*- 2 3 // Copyright (C) 2004-2025 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 #ifdef _GLIBCXX_SYSHDR 34 #pragma GCC system_header 35 #endif 36 37 #if __cplusplus >= 201103L 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 #if __glibcxx_reference_wrapper >= 202403L // >= C++26 44 # include <compare> 45 #endif 46 47 namespace std _GLIBCXX_VISIBILITY(default) 48 { 49 _GLIBCXX_BEGIN_NAMESPACE_VERSION 50 51 /// @cond undocumented 52 53 /** 54 * Derives from @c unary_function or @c binary_function, or perhaps 55 * nothing, depending on the number of arguments provided. The 56 * primary template is the basis case, which derives nothing. 57 */ 58 template<typename _Res, typename... _ArgTypes> 59 struct _Maybe_unary_or_binary_function { }; 60 61 // Ignore warnings about unary_function and binary_function. 62 #pragma GCC diagnostic push 63 #pragma GCC diagnostic ignored "-Wdeprecated-declarations" 64 65 /// Derives from @c unary_function, as appropriate. 66 template<typename _Res, typename _T1> 67 struct _Maybe_unary_or_binary_function<_Res, _T1> 68 : std::unary_function<_T1, _Res> { }; 69 70 /// Derives from @c binary_function, as appropriate. 71 template<typename _Res, typename _T1, typename _T2> 72 struct _Maybe_unary_or_binary_function<_Res, _T1, _T2> 73 : std::binary_function<_T1, _T2, _Res> { }; 74 75 #pragma GCC diagnostic pop 76 77 template<typename _Signature> 78 struct _Mem_fn_traits; 79 80 template<typename _Res, typename _Class, typename... _ArgTypes> 81 struct _Mem_fn_traits_base 82 { 83 using __result_type = _Res; 84 using __maybe_type 85 = _Maybe_unary_or_binary_function<_Res, _Class*, _ArgTypes...>; 86 using __arity = integral_constant<size_t, sizeof...(_ArgTypes)>; 87 }; 88 89 #define _GLIBCXX_MEM_FN_TRAITS2(_CV, _REF, _LVAL, _RVAL) \ 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 = false_type; \ 95 }; \ 96 template<typename _Res, typename _Class, typename... _ArgTypes> \ 97 struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes..., ...) _CV _REF> \ 98 : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...> \ 99 { \ 100 using __vararg = true_type; \ 101 }; 102 103 #define _GLIBCXX_MEM_FN_TRAITS(_REF, _LVAL, _RVAL) \ 104 _GLIBCXX_MEM_FN_TRAITS2( , _REF, _LVAL, _RVAL) \ 105 _GLIBCXX_MEM_FN_TRAITS2(const , _REF, _LVAL, _RVAL) \ 106 _GLIBCXX_MEM_FN_TRAITS2(volatile , _REF, _LVAL, _RVAL) \ 107 _GLIBCXX_MEM_FN_TRAITS2(const volatile, _REF, _LVAL, _RVAL) 108 109 _GLIBCXX_MEM_FN_TRAITS( , true_type, true_type) 110 _GLIBCXX_MEM_FN_TRAITS(&, true_type, false_type) 111 _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type) 112 113 #if __cplusplus > 201402L 114 _GLIBCXX_MEM_FN_TRAITS(noexcept, true_type, true_type) 115 _GLIBCXX_MEM_FN_TRAITS(& noexcept, true_type, false_type) 116 _GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type) 117 #endif 118 119 #undef _GLIBCXX_MEM_FN_TRAITS 120 #undef _GLIBCXX_MEM_FN_TRAITS2 121 122 /// If we have found a result_type, extract it. 123 template<typename _Functor, typename = __void_t<>> 124 struct _Maybe_get_result_type 125 { }; 126 127 template<typename _Functor> 128 struct _Maybe_get_result_type<_Functor, 129 __void_t<typename _Functor::result_type>> 130 { typedef typename _Functor::result_type result_type; }; 131 132 /** 133 * Base class for any function object that has a weak result type, as 134 * defined in 20.8.2 [func.require] of C++11. 135 */ 136 template<typename _Functor> 137 struct _Weak_result_type_impl 138 : _Maybe_get_result_type<_Functor> 139 { }; 140 141 /// Retrieve the result type for a function type. 142 template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> 143 struct _Weak_result_type_impl<_Res(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL> 144 { typedef _Res result_type; }; 145 146 /// Retrieve the result type for a varargs function type. 147 template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> 148 struct _Weak_result_type_impl<_Res(_ArgTypes..., 149 ...) _GLIBCXX_NOEXCEPT_QUAL> 150 { typedef _Res result_type; }; 151 152 /// Retrieve the result type for a function pointer. 153 template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> 154 struct _Weak_result_type_impl<_Res(*)(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL> 155 { typedef _Res result_type; }; 156 157 /// Retrieve the result type for a varargs function pointer. 158 template<typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM> 159 struct 160 _Weak_result_type_impl<_Res(*)(_ArgTypes..., ...) _GLIBCXX_NOEXCEPT_QUAL> 161 { typedef _Res result_type; }; 162 163 // Let _Weak_result_type_impl perform the real work. 164 template<typename _Functor, 165 bool = is_member_function_pointer<_Functor>::value> 166 struct _Weak_result_type_memfun 167 : _Weak_result_type_impl<_Functor> 168 { }; 169 170 // A pointer to member function has a weak result type. 171 template<typename _MemFunPtr> 172 struct _Weak_result_type_memfun<_MemFunPtr, true> 173 { 174 using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type; 175 }; 176 177 // A pointer to data member doesn't have a weak result type. 178 template<typename _Func, typename _Class> 179 struct _Weak_result_type_memfun<_Func _Class::*, false> 180 { }; 181 182 /** 183 * Strip top-level cv-qualifiers from the function object and let 184 * _Weak_result_type_memfun perform the real work. 185 */ 186 template<typename _Functor> 187 struct _Weak_result_type 188 : _Weak_result_type_memfun<typename remove_cv<_Functor>::type> 189 { }; 190 191 #if __cplusplus <= 201703L 192 // Detect nested argument_type. 193 template<typename _Tp, typename = __void_t<>> 194 struct _Refwrap_base_arg1 195 { }; 196 197 // Nested argument_type. 198 template<typename _Tp> 199 struct _Refwrap_base_arg1<_Tp, 200 __void_t<typename _Tp::argument_type>> 201 { 202 typedef typename _Tp::argument_type argument_type; 203 }; 204 205 // Detect nested first_argument_type and second_argument_type. 206 template<typename _Tp, typename = __void_t<>> 207 struct _Refwrap_base_arg2 208 { }; 209 210 // Nested first_argument_type and second_argument_type. 211 template<typename _Tp> 212 struct _Refwrap_base_arg2<_Tp, 213 __void_t<typename _Tp::first_argument_type, 214 typename _Tp::second_argument_type>> 215 { 216 typedef typename _Tp::first_argument_type first_argument_type; 217 typedef typename _Tp::second_argument_type second_argument_type; 218 }; 219 220 /** 221 * Derives from unary_function or binary_function when it 222 * can. Specializations handle all of the easy cases. The primary 223 * template determines what to do with a class type, which may 224 * derive from both unary_function and binary_function. 225 */ 226 template<typename _Tp> 227 struct _Reference_wrapper_base 228 : _Weak_result_type<_Tp>, _Refwrap_base_arg1<_Tp>, _Refwrap_base_arg2<_Tp> 229 { }; 230 231 // Ignore warnings about unary_function and binary_function. 232 #pragma GCC diagnostic push 233 #pragma GCC diagnostic ignored "-Wdeprecated-declarations" 234 235 // - a function type (unary) 236 template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM> 237 struct _Reference_wrapper_base<_Res(_T1) _GLIBCXX_NOEXCEPT_QUAL> 238 : unary_function<_T1, _Res> 239 { }; 240 241 template<typename _Res, typename _T1> 242 struct _Reference_wrapper_base<_Res(_T1) const> 243 : unary_function<_T1, _Res> 244 { }; 245 246 template<typename _Res, typename _T1> 247 struct _Reference_wrapper_base<_Res(_T1) volatile> 248 : unary_function<_T1, _Res> 249 { }; 250 251 template<typename _Res, typename _T1> 252 struct _Reference_wrapper_base<_Res(_T1) const volatile> 253 : unary_function<_T1, _Res> 254 { }; 255 256 // - a function type (binary) 257 template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM> 258 struct _Reference_wrapper_base<_Res(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL> 259 : binary_function<_T1, _T2, _Res> 260 { }; 261 262 template<typename _Res, typename _T1, typename _T2> 263 struct _Reference_wrapper_base<_Res(_T1, _T2) const> 264 : binary_function<_T1, _T2, _Res> 265 { }; 266 267 template<typename _Res, typename _T1, typename _T2> 268 struct _Reference_wrapper_base<_Res(_T1, _T2) volatile> 269 : binary_function<_T1, _T2, _Res> 270 { }; 271 272 template<typename _Res, typename _T1, typename _T2> 273 struct _Reference_wrapper_base<_Res(_T1, _T2) const volatile> 274 : binary_function<_T1, _T2, _Res> 275 { }; 276 277 // - a function pointer type (unary) 278 template<typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM> 279 struct _Reference_wrapper_base<_Res(*)(_T1) _GLIBCXX_NOEXCEPT_QUAL> 280 : unary_function<_T1, _Res> 281 { }; 282 283 // - a function pointer type (binary) 284 template<typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM> 285 struct _Reference_wrapper_base<_Res(*)(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL> 286 : binary_function<_T1, _T2, _Res> 287 { }; 288 289 template<typename _Tp, bool = is_member_function_pointer<_Tp>::value> 290 struct _Reference_wrapper_base_memfun 291 : _Reference_wrapper_base<_Tp> 292 { }; 293 294 template<typename _MemFunPtr> 295 struct _Reference_wrapper_base_memfun<_MemFunPtr, true> 296 : _Mem_fn_traits<_MemFunPtr>::__maybe_type 297 { 298 using result_type = typename _Mem_fn_traits<_MemFunPtr>::__result_type; 299 }; 300 #pragma GCC diagnostic pop 301 #endif // ! C++20 302 303 /// @endcond 304 305 /** 306 * @brief Primary class template for reference_wrapper. 307 * @ingroup functors 308 */ 309 template<typename _Tp> 310 class reference_wrapper 311 #if __cplusplus <= 201703L 312 // In C++20 std::reference_wrapper<T> allows T to be incomplete, 313 // so checking for nested types could result in ODR violations. 314 : public _Reference_wrapper_base_memfun<typename remove_cv<_Tp>::type> 315 #endif 316 { 317 _Tp* _M_data; 318 319 _GLIBCXX20_CONSTEXPR 320 static _Tp* _S_fun(_Tp& __r) noexcept { return std::__addressof(__r); } 321 322 static void _S_fun(_Tp&&) = delete; 323 324 template<typename _Up, typename _Up2 = __remove_cvref_t<_Up>> 325 using __not_same 326 = typename enable_if<!is_same<reference_wrapper, _Up2>::value>::type; 327 328 public: 329 typedef _Tp type; 330 331 // _GLIBCXX_RESOLVE_LIB_DEFECTS 332 // 2993. reference_wrapper<T> conversion from T&& 333 // 3041. Unnecessary decay in reference_wrapper 334 template<typename _Up, typename = __not_same<_Up>, typename 335 = decltype(reference_wrapper::_S_fun(std::declval<_Up>()))> 336 _GLIBCXX20_CONSTEXPR 337 reference_wrapper(_Up&& __uref) 338 noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>()))) 339 : _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref))) 340 { } 341 342 reference_wrapper(const reference_wrapper&) = default; 343 344 reference_wrapper& 345 operator=(const reference_wrapper&) = default; 346 347 _GLIBCXX20_CONSTEXPR 348 operator _Tp&() const noexcept 349 { return this->get(); } 350 351 _GLIBCXX20_CONSTEXPR 352 _Tp& 353 get() const noexcept 354 { return *_M_data; } 355 356 template<typename... _Args> 357 _GLIBCXX20_CONSTEXPR 358 typename __invoke_result<_Tp&, _Args...>::type 359 operator()(_Args&&... __args) const 360 noexcept(__is_nothrow_invocable<_Tp&, _Args...>::value) 361 { 362 #if __cplusplus > 201703L 363 if constexpr (is_object_v<type>) 364 static_assert(sizeof(type), "type must be complete"); 365 #endif 366 return std::__invoke(get(), std::forward<_Args>(__args)...); 367 } 368 369 #if __glibcxx_reference_wrapper >= 202403L // >= C++26 370 // [refwrap.comparisons], comparisons 371 [[nodiscard]] 372 friend constexpr bool 373 operator==(reference_wrapper __x, reference_wrapper __y) 374 requires requires { { __x.get() == __y.get() } -> convertible_to<bool>; } 375 { return __x.get() == __y.get(); } 376 377 [[nodiscard]] 378 friend constexpr bool 379 operator==(reference_wrapper __x, const _Tp& __y) 380 requires requires { { __x.get() == __y } -> convertible_to<bool>; } 381 { return __x.get() == __y; } 382 383 [[nodiscard]] 384 friend constexpr bool 385 operator==(reference_wrapper __x, reference_wrapper<const _Tp> __y) 386 requires (!is_const_v<_Tp>) 387 && requires { { __x.get() == __y.get() } -> convertible_to<bool>; } 388 { return __x.get() == __y.get(); } 389 390 // _GLIBCXX_RESOLVE_LIB_DEFECTS 391 // 4071. reference_wrapper comparisons are not SFINAE-friendly 392 393 [[nodiscard]] 394 friend constexpr auto 395 operator<=>(reference_wrapper __x, reference_wrapper __y) 396 requires requires (const _Tp __t) { 397 { __t < __t } -> __detail::__boolean_testable; 398 } 399 { return __detail::__synth3way(__x.get(), __y.get()); } 400 401 [[nodiscard]] 402 friend constexpr auto 403 operator<=>(reference_wrapper __x, const _Tp& __y) 404 requires requires { { __y < __y } -> __detail::__boolean_testable; } 405 { return __detail::__synth3way(__x.get(), __y); } 406 407 [[nodiscard]] 408 friend constexpr auto 409 operator<=>(reference_wrapper __x, reference_wrapper<const _Tp> __y) 410 requires (!is_const_v<_Tp>) && requires (const _Tp __t) { 411 { __t < __t } -> __detail::__boolean_testable; 412 } 413 { return __detail::__synth3way(__x.get(), __y.get()); } 414 #endif 415 }; 416 417 #if __cpp_deduction_guides 418 template<typename _Tp> 419 reference_wrapper(_Tp&) -> reference_wrapper<_Tp>; 420 #endif 421 422 /// @relates reference_wrapper @{ 423 424 /// Denotes a reference should be taken to a variable. 425 template<typename _Tp> 426 _GLIBCXX20_CONSTEXPR 427 inline reference_wrapper<_Tp> 428 ref(_Tp& __t) noexcept 429 { return reference_wrapper<_Tp>(__t); } 430 431 /// Denotes a const reference should be taken to a variable. 432 template<typename _Tp> 433 _GLIBCXX20_CONSTEXPR 434 inline reference_wrapper<const _Tp> 435 cref(const _Tp& __t) noexcept 436 { return reference_wrapper<const _Tp>(__t); } 437 438 template<typename _Tp> 439 void ref(const _Tp&&) = delete; 440 441 template<typename _Tp> 442 void cref(const _Tp&&) = delete; 443 444 /// std::ref overload to prevent wrapping a reference_wrapper 445 template<typename _Tp> 446 _GLIBCXX20_CONSTEXPR 447 inline reference_wrapper<_Tp> 448 ref(reference_wrapper<_Tp> __t) noexcept 449 { return __t; } 450 451 /// std::cref overload to prevent wrapping a reference_wrapper 452 template<typename _Tp> 453 _GLIBCXX20_CONSTEXPR 454 inline reference_wrapper<const _Tp> 455 cref(reference_wrapper<_Tp> __t) noexcept 456 { return { __t.get() }; } 457 458 /// @} 459 460 _GLIBCXX_END_NAMESPACE_VERSION 461 } // namespace std 462 463 #endif // C++11 464 465 #endif // _GLIBCXX_REFWRAP_H
