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

   1 // Pointer Traits -*- C++ -*-
   2
   3 // Copyright (C) 2011-2024 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 bits/ptr_traits.h
  26  *  This is an internal header file, included by other library headers.
  27  *  Do not attempt to use it directly. @headername{memory}
  28  */
  29
  30 #ifndef _PTR_TRAITS_H
  31 #define _PTR_TRAITS_H 1
  32
  33 #if __cplusplus >= 201103L
  34
  35 #include <bits/move.h>
  36
  37 #if __cplusplus > 201703L
  38 #include <concepts>
  39 namespace __gnu_debug { struct _Safe_iterator_base; }
  40 #endif
  41
  42 namespace std _GLIBCXX_VISIBILITY(default)
  43 {
  44 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  45
  46   /// @cond undocumented
  47
  48   class __undefined;
  49
  50   // For a specialization `SomeTemplate<T, Types...>` the member `type` is T,
  51   // otherwise `type` is `__undefined`.
  52   template<typename _Tp>
  53     struct __get_first_arg
  54     { using type = __undefined; };
  55
  56   template<template<typename, typename...> class _SomeTemplate, typename _Tp,
  57            typename... _Types>
  58     struct __get_first_arg<_SomeTemplate<_Tp, _Types...>>
  59     { using type = _Tp; };
  60
  61   // For a specialization `SomeTemplate<T, Args...>` and a type `U` the member
  62   // `type` is `SomeTemplate<U, Args...>`, otherwise there is no member `type`.
  63   template<typename _Tp, typename _Up>
  64     struct __replace_first_arg
  65     { };
  66
  67   template<template<typename, typename...> class _SomeTemplate, typename _Up,
  68            typename _Tp, typename... _Types>
  69     struct __replace_first_arg<_SomeTemplate<_Tp, _Types...>, _Up>
  70     { using type = _SomeTemplate<_Up, _Types...>; };
  71
  72   // Detect the element type of a pointer-like type.
  73   template<typename _Ptr, typename = void>
  74     struct __ptr_traits_elem : __get_first_arg<_Ptr>
  75     { };
  76
  77   // Use _Ptr::element_type if is a valid type.
  78 #if __cpp_concepts
  79   template<typename _Ptr> requires requires { typename _Ptr::element_type; }
  80     struct __ptr_traits_elem<_Ptr, void>
  81     { using type = typename _Ptr::element_type; };
  82 #else
  83   template<typename _Ptr>
  84     struct __ptr_traits_elem<_Ptr, __void_t<typename _Ptr::element_type>>
  85     { using type = typename _Ptr::element_type; };
  86 #endif
  87
  88   template<typename _Ptr>
  89     using __ptr_traits_elem_t = typename __ptr_traits_elem<_Ptr>::type;
  90
  91   /// @endcond
  92
  93   // Define pointer_traits<P>::pointer_to.
  94   template<typename _Ptr, typename _Elt, bool = is_void<_Elt>::value>
  95     struct __ptr_traits_ptr_to
  96     {
  97       using pointer = _Ptr;
  98       using element_type = _Elt;
  99
 100       /**
 101        *  @brief  Obtain a pointer to an object
 102        *  @param  __r  A reference to an object of type `element_type`
 103        *  @return `pointer::pointer_to(__r)`
 104        *  @pre `pointer::pointer_to(__r)` is a valid expression.
 105       */
 106       static pointer
 107       pointer_to(element_type& __r)
 108 #if __cpp_lib_concepts
 109       requires requires {
 110         { pointer::pointer_to(__r) } -> convertible_to<pointer>;
 111       }
 112 #endif
 113       { return pointer::pointer_to(__r); }
 114     };
 115
 116   // Do not define pointer_traits<P>::pointer_to if element type is void.
 117   template<typename _Ptr, typename _Elt>
 118     struct __ptr_traits_ptr_to<_Ptr, _Elt, true>
 119     { };
 120
 121   // Partial specialization defining pointer_traits<T*>::pointer_to(T&).
 122   template<typename _Tp>
 123     struct __ptr_traits_ptr_to<_Tp*, _Tp, false>
 124     {
 125       using pointer = _Tp*;
 126       using element_type = _Tp;
 127
 128       /**
 129        *  @brief  Obtain a pointer to an object
 130        *  @param  __r  A reference to an object of type `element_type`
 131        *  @return `addressof(__r)`
 132       */
 133       static _GLIBCXX20_CONSTEXPR pointer
 134       pointer_to(element_type& __r) noexcept
 135       { return std::addressof(__r); }
 136     };
 137
 138   template<typename _Ptr, typename _Elt>
 139     struct __ptr_traits_impl : __ptr_traits_ptr_to<_Ptr, _Elt>
 140     {
 141     private:
 142       template<typename _Tp>
 143         using __diff_t = typename _Tp::difference_type;
 144
 145       template<typename _Tp, typename _Up>
 146         using __rebind = __type_identity<typename _Tp::template rebind<_Up>>;
 147
 148     public:
 149       /// The pointer type.
 150       using pointer = _Ptr;
 151
 152       /// The type pointed to.
 153       using element_type = _Elt;
 154
 155       /// The type used to represent the difference between two pointers.
 156       using difference_type = __detected_or_t<ptrdiff_t, __diff_t, _Ptr>;
 157
 158       /// A pointer to a different type.
 159       template<typename _Up>
 160         using rebind = typename __detected_or_t<__replace_first_arg<_Ptr, _Up>,
 161                                                 __rebind, _Ptr, _Up>::type;
 162     };
 163
 164   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 165   // 3545. std::pointer_traits should be SFINAE-friendly
 166   template<typename _Ptr>
 167     struct __ptr_traits_impl<_Ptr, __undefined>
 168     { };
 169
 170   /**
 171    * @brief  Uniform interface to all pointer-like types
 172    * @headerfile memory
 173    * @ingroup pointer_abstractions
 174    * @since C++11
 175   */
 176   template<typename _Ptr>
 177     struct pointer_traits : __ptr_traits_impl<_Ptr, __ptr_traits_elem_t<_Ptr>>
 178     { };
 179
 180   /**
 181    * @brief  Partial specialization for built-in pointers.
 182    * @headerfile memory
 183    * @ingroup pointer_abstractions
 184    * @since C++11
 185   */
 186   template<typename _Tp>
 187     struct pointer_traits<_Tp*> : __ptr_traits_ptr_to<_Tp*, _Tp>
 188     {
 189       /// The pointer type
 190       typedef _Tp* pointer;
 191       /// The type pointed to
 192       typedef _Tp  element_type;
 193       /// Type used to represent the difference between two pointers
 194       typedef ptrdiff_t difference_type;
 195       /// A pointer to a different type.
 196       template<typename _Up> using rebind = _Up*;
 197     };
 198
 199   /// Convenience alias for rebinding pointers.
 200   template<typename _Ptr, typename _Tp>
 201     using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
 202
 203 #ifndef __glibcxx_to_address // C++ < 20
 204   template<typename _Tp>
 205     [[__gnu__::__always_inline__]]
 206     constexpr _Tp*
 207     __to_address(_Tp* __ptr) noexcept
 208     {
 209       static_assert(!std::is_function<_Tp>::value, "std::to_address argument "
 210                     "must not be a function pointer");
 211       return __ptr;
 212     }
 213
 214   template<typename _Ptr>
 215     constexpr typename std::pointer_traits<_Ptr>::element_type*
 216     __to_address(const _Ptr& __ptr)
 217     { return std::__to_address(__ptr.operator->()); }
 218 #else
 219   /**
 220    * @brief Obtain address referenced by a pointer to an object
 221    * @param __ptr A pointer to an object
 222    * @return @c __ptr
 223    * @ingroup pointer_abstractions
 224   */
 225   template<typename _Tp>
 226     [[__gnu__::__always_inline__]]
 227     constexpr _Tp*
 228     to_address(_Tp* __ptr) noexcept
 229     {
 230       static_assert(!is_function_v<_Tp>, "std::to_address argument "
 231                     "must not be a function pointer");
 232       return __ptr;
 233     }
 234
 235   /**
 236    * @brief Obtain address referenced by a pointer to an object
 237    * @param __ptr A pointer to an object
 238    * @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
 239              well-formed, otherwise @c to_address(__ptr.operator->())
 240    * @ingroup pointer_abstractions
 241   */
 242   template<typename _Ptr>
 243     constexpr auto
 244     to_address(const _Ptr& __ptr) noexcept
 245     {
 246       if constexpr (requires { pointer_traits<_Ptr>::to_address(__ptr); })
 247         return pointer_traits<_Ptr>::to_address(__ptr);
 248       else if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
 249         return std::to_address(__ptr.base().operator->());
 250       else
 251         return std::to_address(__ptr.operator->());
 252     }
 253
 254   /// @cond undocumented
 255   /// Compatibility for use in code that is also compiled as pre-C++20.
 256   template<typename _Ptr>
 257     [[__gnu__::__always_inline__]]
 258     constexpr auto
 259     __to_address(const _Ptr& __ptr) noexcept
 260     { return std::to_address(__ptr); }
 261   /// @endcond
 262 #endif // __glibcxx_to_address
 263
 264 _GLIBCXX_END_NAMESPACE_VERSION
 265 } // namespace std
 266
 267 #endif
 268
 269 #endif