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[MNT]: Re-enable Automatic Reference Counting (ARC) for macOS backend. #31797
Description
Summary
@greglucas mentioned that he is interested in moving the macOS backend to ARC. This was previously attempted in #23060, caused a crash in #23653, and reverted in #23654.
After my memory-management PR lands, enabling ARC should be relatively straightforward.
The one issue is that we store Obj-C objects into C structs (allocated by tp_alloc). Support for ARC objects in C structs wasn't added until macOS 10.14 / Xcode 10. We support compiling on macOS 10.12.
Additionally, even if we changed our minimum macOS to 10.14, we would need to ensure that tp_alloc guarantees zero-filled memory to be compatible with the Xcode 10 feature.
In the meantime, we will have to use an __unsafe_unretained attribute on the objects in our C structs, and manually retain/release them.
Proposed fix
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Activity
iccir commented on May 31, 2026
Adding this comment mostly for my own future reference.
WWDC 2018 Session 409 explains the "ARC in C Structs" feature added in Xcode 10. Apple likes to remove old WWDC videos, so here's links to the Archived Video (warning, 1.3GB download) and Archived Slides.