[GitHub] [arrow] bkietz commented on pull request #37713: GH-37670: [C++] S3 IO Output extend from enable_shared_from_this

["bkietz (via GitHub)" <gi...@apache.org>]

bkietz commented on PR #37713:
URL: https://github.com/apache/arrow/pull/37713#issuecomment-1724150628

   `dynamic_pointer_cast` is indeed necessary to move `shared_from_this` to `FileInterface`. AFAIU, this shouldn't cause any problems (technically `enable_shared_from_this` will not be a virtual base, only `FileInterface` is); `enable_shared_from_this` is usually implemented as a data member [private weak pointer to itself](https://github.com/llvm/llvm-project/blob/main/libcxx/include/__memory/shared_ptr.h#L1914) so we don't need to worry about `offsetof` hackery falling down.


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