| ========================================= |
| Libc++ 12.0.0 (In-Progress) Release Notes |
| ========================================= |
| |
| .. contents:: |
| :local: |
| :depth: 2 |
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| Written by the `Libc++ Team <https://libcxx.llvm.org>`_ |
| |
| .. warning:: |
| |
| These are in-progress notes for the upcoming libc++ 12 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 12.0.0. 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++ 12.0.0? |
| ============================ |
| |
| New Features |
| ------------ |
| |
| - ... |
| |
| API Changes |
| ----------- |
| - By default, libc++ will _not_ include the definition for new and delete, |
| since those are provided in libc++abi. Vendors wishing to provide new and |
| delete in libc++ can build the library with ``-DLIBCXX_ENABLE_NEW_DELETE_DEFINITIONS=ON`` |
| to get back the old behavior. This was done to avoid providing new and delete |
| in both libc++ and libc++abi, which is technically an ODR violation. Also |
| note that we couldn't decide to put the operators in libc++ only, because |
| they are needed from libc++abi (which would create a circular dependency). |
| - During the C++20 standardization process some new low-level bit functions |
| have been renamed. Libc++ has renamed these functions to match the C++20 |
| Standard. |
| - ``ispow2`` has been renamed to ``has_single_bit`` |
| - ``ceil2`` has been renamed to ``bit_ceil`` |
| - ``floor2`` has been renamed to ``bit_floor`` |
| - ``log2p1`` has been renamed to ``bit_width`` |
| |
| - In C++20 mode, ``std::filesystem::path::u8string()`` and |
| ``generic_u8string()`` now return ``std::u8string`` according to P0428, |
| while they return ``std::string`` in C++17. This can cause source |
| incompatibility, which is discussed and acknowledged in P1423, but that |
| paper doesn't suggest any remediation for this incompatibility. |