Borrowing Accessors

[tbkka]

Following the [Prospective Vision] Accessors
we're now ready to formally propose borrow and mutate accessors which allow a property or subscript to return a borrowed value with full exclusivity safety checks.

[benrimmington]

Swift Collections fails to compile (Swift 6.2.3, Xcode 26.2) when the yielding CoroutineAccessors experimental feature (SE-0474) is enabled.

Error: anonymous closure argument not contained in a closure

https://github.com/apple/swift-collections/blob/1.3.0/Sources/HashTreeCollections/HashNode/_HashNode.swift#L104

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Swift Collections also has borrow() and mutate() methods, but they don't take trailing closures.

https://github.com/apple/swift-collections/blob/1.3.0/Sources/ContainersPreview/Box.swift#L109

[tbkka]

The final SE-0474 switched to yielding borrow and yielding mutate. The PR to implement the new terms is swiftlang/swift#86277. So the issue you describe here should be resolved by that.

We started to experiment with parser-level approaches to disambiguate such cases while working on the implementation of SE-0474 but then instead changed the keywords to avoid it. We may need to revisit those ideas for these borrowing accessors.

[tbkka]

CC: @meg-gupta