Libc++ 21.0.0 (In-Progress) Release Notes

Written by the Libc++ Team

Warning

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. All LLVM releases may be downloaded from the LLVM releases web site.

For more information about libc++, please see the Libc++ Web Site 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++ 21.0.0?

Implemented Papers

  • N4258: Cleaning-up noexcept in the Library (Github)

  • P0767R1: Deprecate POD (Github)

  • P1361R2: Integration of chrono with text formatting (Github)

  • P2255R2: A type trait to detect reference binding to temporary (implemented the type traits only) (Github)

  • P2562R1: constexpr Stable Sorting (Github)

  • P1222R4: A Standard flat_set is partially implemented and flat_set is provided (Github)

  • P0472R3: Put std::monostate in <utility> (Github)

Improvements and New Features

  • The std::ranges::{copy, copy_n, copy_backward, move, move_backward, rotate} algorithms have been optimized for std::vector<bool>::iterator, resulting in a performance improvement of up to 2000x.

  • The std::ranges::equal algorithm has been optimized for std::vector<bool>::iterator, resulting in a performance improvement of up to 188x.

  • The std::ranges::swap_ranges algorithm has been optimized for std::vector<bool>::iterator, resulting in a performance improvement of up to 611x.

  • Updated formatting library to Unicode 16.0.0.

Deprecations and Removals

  • std::is_pod and std::is_pod_v are deprecated in C++20 and later.

Upcoming Deprecations and Removals

LLVM 22

  • TODO

ABI Affecting Changes

  • When using GCC, the std namespace is now annotated with [[gnu::visibility("default")]]. This may cause more symbols to be exported from shared libraries when building with -fvisibility=hidden. This also fixes RTTI comparison between shared libraries, since all RTTI has the correct visibility now. There is no behaviour change on Clang.

Build System Changes

  • TODO