base/cxx20_to_address.h

   1 // Copyright 2021 The Chromium Authors
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_CXX20_TO_ADDRESS_H_
   6 #define BASE_CXX20_TO_ADDRESS_H_
   7
   8 #include <type_traits>
   9
  10 namespace base {
  11
  12 // Implementation of C++20's std::to_address.
  13 // Note: This does consider specializations of pointer_traits<>::to_address,
  14 // even though it's a C++20 member function, because CheckedContiguousIterator
  15 // specializes pointer_traits<> with a to_address() member.
  16 //
  17 // Reference: https://wg21.link/pointer.conversion#lib:to_address
  18 template <typename T>
  19 constexpr T* to_address(T* p) noexcept {
  20   static_assert(!std::is_function<T>::value,
  21                 "Error: T must not be a function type.");
  22   return p;
  23 }
  24
  25 template <typename Ptr>
  26 constexpr auto to_address(const Ptr& p) noexcept
  27     -> decltype(std::pointer_traits<Ptr>::to_address(p)) {
  28   return std::pointer_traits<Ptr>::to_address(p);
  29 }
  30
  31 template <typename Ptr, typename... None>
  32 constexpr auto to_address(const Ptr& p, None...) noexcept {
  33   return base::to_address(p.operator->());
  34 }
  35
  36 }  // namespace base
  37
  38 #endif  // BASE_CXX20_TO_ADDRESS_H_