libcxx/docs/ReleaseNotes/24.rst

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Libc++ 24.0.0 Release Notes
===========================

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Written by the `Libc++ Team <https://libcxx.llvm.org>`_

.. warning::

   These are in-progress notes for the upcoming libc++ 24.0.0 release.
   Release notes for previous releases can be found on
   `the Download Page <https://releases.llvm.org/download.html>`_.

Introduction
============

This document contains the release notes for the libc++ C++ Standard Library,
part of the LLVM Compiler Infrastructure, release 24.0.0. 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 <https://llvm.org/releases/>`_.

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

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 <https://llvm.org/releases/>`_.

What's New in Libc++ 24.0.0?
==============================

Implemented Papers
------------------

- P0493R5: Atomic minimum/maximum (`Github <https://llvm.org/PR105418>`__)
- P0792R14: ``function_ref`` : a type-erased callable reference (`Github <https://llvm.org/PR105376>`__)
- P3948R1: ``constant_wrapper`` is the only tool needed for passing constant expressions via function arguments (`Github <https://llvm.org/PR189604>`__)
- P3961R1: Less double indirection in ``function_ref`` (RU-220) (`Github <https://llvm.org/PR189606>`__)
- P1901R2: Enabling the Use of ``weak_ptr`` as Keys in Unordered Associative Containers (`Github <https://llvm.org/PR105372>`__)
- P0528R3: The Curious Case of Padding Bits, Featuring Atomic Compare-and-Exchange (`Github <https://llvm.org/PR76180>`__)

Improvements and New Features
-----------------------------


Deprecations and Removals
-------------------------

- The ``std::launch::any`` enumerator that was accidentally provided as an extension is now deprecated.
  It will be removed in LLVM 25.

Potentially breaking changes
----------------------------

- TODO: In LLVM 23, libc++ dropped a lot of transitive includes in all language modes. This improves compile time significantly,
  but causes programs which rely on these includes to not compile anymore. The ``_LIBCPP_KEEP_TRANSITIVE_INCLUDES_LLVM23``
  macro that was provided in LLVM 23 to ease the transition has been removed in this release.

Announcements About Future Releases
-----------------------------------

- ``std::allocator`` is trivially default constructible since LLVM 22. In LLVM 23 and LLVM 24, the
  ``_LIBCPP_DEPRECATED_ABI_NON_TRIVIAL_ALLOCATOR`` macro was provided as an escape hatch to revert that change.
  This escape hatch will be removed in LLVM 25 if there is no evidence of it being useful.

- ``bitset::operator[]`` returns ``bool`` since LLVM 22, fixing a conformance bug. In LLVM 23 and LLVM 24, the
  ``_LIBCPP_DEPRECATED_ABI_BITSET_CONST_SUBSCRIPT_RETURN_REF`` macro was provided as an escape hatch to revert
  that change. This escape hatch will be removed in LLVM 25 if there is no evidence of it being useful.

ABI Affecting Changes
---------------------

Build System Changes
--------------------