=========================================== Libc++ 20.0.0 (In-Progress) Release Notes

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Written by the Libc++ Team

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These are in-progress notes for the upcoming libc++ 20.0.0 release. Release notes for previous releases can be found on the Download Page.

Introduction

This document contains the release notes for the libc++ C++ Standard Library, part of the LLVM Compiler Infrastructure, release 20.0.0. Here we describe the status of libc++ in some detail, including major improvements from the previous release and new feature work. For the general LLVM release notes, see the LLVM documentation <https://llvm.org/docs/ReleaseNotes.html>_. All LLVM releases may be downloaded from the LLVM releases web site.

For more information about libc++, please see the Libc++ Web Site <https://libcxx.llvm.org>_ or the LLVM Web Site.

Note that if you are reading this file from a Git checkout or the main Libc++ web page, this document applies to the next release, not the current one. To see the release notes for a specific release, please see the releases page.

What's New in Libc++ 20.0.0?

Implemented Papers

• TODO

Improvements and New Features

• TODO

Deprecations and Removals

• TODO: The LIBCXX_ENABLE_ASSERTIONS CMake variable and the _LIBCPP_ENABLE_ASSERTIONS macro that were used to enable the safe mode will be removed in LLVM 20.

• TODO: The C++20 synchronization library will be removed entirely in language modes prior to C++20 in LLVM 20.

• TODO: The relational operators for std::chrono::weekday will be removed entirely, and the _LIBCPP_ENABLE_REMOVED_WEEKDAY_RELATIONAL_OPERATORS macro that was used to re-enable this extension will be ignored in LLVM 20.

• TODO: The _LIBCPP_ENABLE_REMOVED_ALLOCATOR_CONST macro will no longer have an effect.

Upcoming Deprecations and Removals

LLVM 20

- TODO


LLVM 21

• The status of the C++03 implementation will be frozen after the LLVM 21 release. This means that starting in LLVM 22, non-critical bug fixes may not be back-ported to C++03, including LWG issues. C++03 is a legacy platform, where most projects are no longer actively maintained. To reduce the amount of fixes required to keep such legacy projects compiling with up-to-date toolchains, libc++ will aim to freeze the status of the headers in C++03 mode to avoid unintended breaking changes. See https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc for more details.

  If you are using C++03 in your project, you should consider moving to a newer version of the Standard to get the most out of libc++.

ABI Affecting Changes

• TODO

Build System Changes

• TODO