webrtc/rtc_base/system/no_unique_address.h
Peter Kasting 662d7f11d5 Fixes to support building in -std=c++20 mode.
* Structs with user-declared constructors are no longer considered
  aggregates, so remove the declarations when possible
* Types of both arguments to "==" must match to avoid "ambiguous
  function call" warning
* Various types of math involving enums are deprecated, so replace with
  constexprs where necessary
* ABSL_CONST_INIT must be used on definition as well as declaration
* volatile memory may no longer be read from and written to by the same
  operator, so replace e.g. "n++" with "n = n + 1"
* Replace an outdated check for no_unique_address support with
  __has_cpp_attribute
* std::result_of(f(x)) has been removed, replace with
  std::invoke_result(f, x)

Bug: chromium:1284275
Change-Id: I77b366ab1da7eb2c1e4c825b2714417c31ee5903
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261221
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Tomas Gunnarsson <tommi@google.com>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36786}
2022-05-05 17:15:58 +00:00

37 lines
1.6 KiB
C++

/*
* Copyright (c) 2020 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef RTC_BASE_SYSTEM_NO_UNIQUE_ADDRESS_H_
#define RTC_BASE_SYSTEM_NO_UNIQUE_ADDRESS_H_
// RTC_NO_UNIQUE_ADDRESS is a portable annotation to tell the compiler that
// a data member need not have an address distinct from all other non-static
// data members of its class.
// It allows empty types to actually occupy zero bytes as class members,
// instead of occupying at least one byte just so that they get their own
// address. There is almost never any reason not to use it on class members
// that could possibly be empty.
// The macro expands to [[no_unique_address]] if the compiler supports the
// attribute, it expands to nothing otherwise.
// Clang should supports this attribute since C++11, while other compilers
// should add support for it starting from C++20. Among clang compilers,
// clang-cl doesn't support it yet and support is unclear also when the target
// platform is iOS.
#ifndef __has_cpp_attribute
#define __has_cpp_attribute(__x) 0
#endif
#if __has_cpp_attribute(no_unique_address)
// NOLINTNEXTLINE(whitespace/braces)
#define RTC_NO_UNIQUE_ADDRESS [[no_unique_address]]
#else
#define RTC_NO_UNIQUE_ADDRESS
#endif
#endif // RTC_BASE_SYSTEM_NO_UNIQUE_ADDRESS_H_