[ObjectiveC] NSObject: Clarify hashing implementation #18257
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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.
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@swift-ci please test |
natecook1000
approved these changes
Jul 26, 2018
DougGregor
approved these changes
Jul 26, 2018
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@DougGregor Yes! I removed the hashValue change from this PR, pending more discussion. I expect to submit a separate PR for it soon. |
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NSObjectdefines its own interface for hashing and equality. Subclasses must implement custom hashing by overriding the hash property, orNSSetandNSDictionarywill not work correctly.Unfortunately, we currently define
NSObject.hashValueandNSObject.hash(into:)as overridable, which leads people to accidentally override one of these instead ofhash.hashValueis explicitly declared open, whilehash(into:)is automatically synthesized as such.Making
hashValuenon-open is a potentially source breaking change, but we can at least provide an explicit, non-overridable definition forhash(into:), and update the documentation to explain the contract.rdar://problem/42623967