[libcxx-commits] [PATCH] D97742: [C++23] [P1518R2] Better CTAD behavior for containers with allocators

[Arthur O'Dwyer via Phabricator via libcxx-commits]

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P1518 <https://reviews.llvm.org/P1518> does the following in C++23 but we'll just do it in C++17 as well:

- Stop requiring `Alloc` to be an allocator on some container-adaptor deduction guides
- Stop deducing from `Allocator` on some sequence container constructors
- Stop deducing from `Allocator` on some other container constructors (libc++ already did this)

The affected constructors are the "allocator-extended" versions of constructors where the non-allocator arguments are already sufficient to deduce the allocator type. For example,

  std::pmr::vector<int> v1;
  std::vector v2(v1, std::pmr::new_delete_resource());
  std::stack s2(v1, std::pmr::new_delete_resource());

P1518R2 (which will be in the next mailing) was adopted, or at least resolved-to-be-adopted, by LWG the other day.

I'm proposing that libc++ implement these CTAD improvements not only in C++2b mode, but also in all modes (i.e. C++17 and C++20). Anyone who doesn't notice won't mind, and anyone who does notice will thank us. Plus, libc++ already implements a little more than half of P1518R2 in all modes. This patch is just getting us all the way there.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97742

Files:
  libcxx/include/deque
  libcxx/include/forward_list
  libcxx/include/list
  libcxx/include/queue
  libcxx/include/stack
  libcxx/include/vector
  libcxx/test/std/containers/container.adaptors/priority.queue/priqueue.cons/deduct.pass.cpp
  libcxx/test/std/containers/container.adaptors/queue/queue.cons/deduct.pass.cpp
  libcxx/test/std/containers/container.adaptors/stack/stack.cons/deduct.pass.cpp
  libcxx/test/std/containers/sequences/deque/deque.cons/deduct.pass.cpp
  libcxx/test/std/containers/sequences/forwardlist/forwardlist.cons/deduct.pass.cpp
  libcxx/test/std/containers/sequences/list/list.cons/deduct.pass.cpp
  libcxx/test/std/containers/sequences/vector/vector.cons/deduct.pass.cpp

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