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 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