libstdc++-v3/include/bits/refwrap.h

   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       static _Tp* _S_fun(_Tp& __r) noexcept { return std::__addressof(__r); }
 295       static void _S_fun(_Tp&&) = delete;
 296
 297       template<typename _Up, typename _Up2 = __remove_cvref_t<_Up>>
 298         using __not_same
 299           = typename enable_if<!is_same<reference_wrapper, _Up2>::value>::type;
 300
 301     public:
 302       typedef _Tp type;
 303
 304       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 305       // 2993. reference_wrapper<T> conversion from T&&
 306       // 3041. Unnecessary decay in reference_wrapper
 307       template<typename _Up, typename = __not_same<_Up>, typename
 308                 = decltype(reference_wrapper::_S_fun(std::declval<_Up>()))>
 309         reference_wrapper(_Up&& __uref)
 310         noexcept(noexcept(reference_wrapper::_S_fun(std::declval<_Up>())))
 311         : _M_data(reference_wrapper::_S_fun(std::forward<_Up>(__uref)))
 312         { }
 313
 314       reference_wrapper(const reference_wrapper&) = default;
 315
 316       reference_wrapper&
 317       operator=(const reference_wrapper&) = default;
 318
 319       operator _Tp&() const noexcept
 320       { return this->get(); }
 321
 322       _Tp&
 323       get() const noexcept
 324       { return *_M_data; }
 325
 326       template<typename... _Args>
 327         typename result_of<_Tp&(_Args&&...)>::type
 328         operator()(_Args&&... __args) const
 329         {
 330           return std::__invoke(get(), std::forward<_Args>(__args)...);
 331         }
 332     };
 333
 334 #if __cpp_deduction_guides
 335   template<typename _Tp>
 336     reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
 337 #endif
 338
 339   /// Denotes a reference should be taken to a variable.
 340   template<typename _Tp>
 341     inline reference_wrapper<_Tp>
 342     ref(_Tp& __t) noexcept
 343     { return reference_wrapper<_Tp>(__t); }
 344
 345   /// Denotes a const reference should be taken to a variable.
 346   template<typename _Tp>
 347     inline reference_wrapper<const _Tp>
 348     cref(const _Tp& __t) noexcept
 349     { return reference_wrapper<const _Tp>(__t); }
 350
 351   template<typename _Tp>
 352     void ref(const _Tp&&) = delete;
 353
 354   template<typename _Tp>
 355     void cref(const _Tp&&) = delete;
 356
 357   /// std::ref overload to prevent wrapping a reference_wrapper
 358   template<typename _Tp>
 359     inline reference_wrapper<_Tp>
 360     ref(reference_wrapper<_Tp> __t) noexcept
 361     { return __t; }
 362
 363   /// std::cref overload to prevent wrapping a reference_wrapper
 364   template<typename _Tp>
 365     inline reference_wrapper<const _Tp>
 366     cref(reference_wrapper<_Tp> __t) noexcept
 367     { return { __t.get() }; }
 368
 369   // @} group functors
 370
 371 _GLIBCXX_END_NAMESPACE_VERSION
 372 } // namespace std
 373
 374 #endif // C++11
 375
 376 #endif // _GLIBCXX_REFWRAP_H