[all-commits] [llvm/llvm-project] 622605: [ADT] Add C++20-style llvm::identity_cxx20 (#164143)

[Kazu Hirata via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 622605e69482862914febfaeaf036aae011e0786
      https://github.com/llvm/llvm-project/commit/622605e69482862914febfaeaf036aae011e0786
  Author: Kazu Hirata <kazu at google.com>
  Date:   2025-10-19 (Sun, 19 Oct 2025)

  Changed paths:
    M llvm/include/llvm/ADT/STLForwardCompat.h
    M llvm/unittests/ADT/STLForwardCompatTest.cpp

  Log Message:
  -----------
  [ADT] Add C++20-style llvm::identity_cxx20 (#164143)

Currently, our llvm::identity<T> is not quite like std::identity from
C++20.  Ours is a template struct while std::identity is a
non-template struct with templatized operator().  This difference
means that we cannot mechanically replace llvm::identity with
std::identity when we switch to C++20 in the future.

This patch implements llvm::identity_cxx20, which behaves exactly like
std::identity.

Once this patch lands, I'm planning to migrate users of llvm::identity
to the new style.  There aren't that many:

- 4 instances of SparseSet<...>
- 3 instances of SparseMultiSet<...>
- about 50 instances of IndexedMap<...>



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