Data.mutableSpan and Data.mutableBytes do not perform uniqueness check #1530
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@swift-ci please test |
kperryua
approved these changes
Oct 1, 2025
glessard
approved these changes
Oct 1, 2025
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| @Test func validateMutation_cow_mutableBytes() { | ||
| var data = Data(Array(repeating: 0, count: 32)) |
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Don't we have Data(count: 32) to get a zero-initialized instance?
Good call, added tests for the large slice too! |
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@swift-ci please test |
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@swift-ci please test |
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@swift-ci please test |
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Unfortunately the
mutableSpanandmutableBytesaccessors onDatado not currently perform a uniqueness check to trigger CoW. This means that you can mutate aDatavia its mutable span even if it references a shared storage. This updates the implementation to trigger CoW for the shared storage representations when accessing the mutable spans as well as a unit test to ensure a copy occurs when not uniquely referenced (and that no copy occurs if the storage is uniquely referenced).