[4.2][ObjectiveC] NSObject: Clarify hashing implementation #18258
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NSObject defines its own interface for hashing and equality. Subclasses must implement custom hashing by overriding the hash property, or NSSet and NSDictionary will not work correctly. Unfortunately, we currently define NSObject.hashValue and NSObject.hash(into:) as overridable, which leads people to accidentally override one of these instead of hash. hashValue is explicitly declared open, while hash(into:) is automatically synthesized as such. Making hashValue non-open is a potentially source breaking change, but we can at least provide an explicit, non-overridable definition for hash(into:), and update the documentation to explain the contract. (cherry picked from commit d03786e)
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@swift-ci please test |
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@swift-ci please nominate |
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Cherry picked from #18257
Explanation:
NSObjectsubclasses must customize hashing by overriding thehashproperty. Provide an explicit, non-overridable definition forNSObject.hash(into:), and update the documentation to explain the contract.Scope: Objective-C interfaces
Issue: rdar://problem/42623967
Risk: Low.
NSObject.hash(into:)is new with Swift 4.2, so making it non-overridable has no source compatibility implications.NSObject.hashValueis left open for now.Testing: Standard test suite.
Reviewed By: @natecook1000 & @DougGregor (#18257)