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[SR-1218] Equatable when inheriting from NSObject #43826

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swift-ci opened this issue Apr 13, 2016 · 1 comment
Closed

[SR-1218] Equatable when inheriting from NSObject #43826

swift-ci opened this issue Apr 13, 2016 · 1 comment
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior.

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@swift-ci
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Previous ID SR-1218
Radar None
Original Reporter mikaoj (JIRA User)
Type Bug
Status Resolved
Resolution Invalid
Environment

Apple Swift version 2.2 (swiftlang-703.0.18.1 clang-703.0.29)
Target: x86_64-apple-macosx10.9

Additional Detail from JIRA
Votes 0
Component/s
Labels Bug
Assignee None
Priority Medium

md5: 4b956b9a294c69ff89786b0f766e9b68

Issue Description:

When you have a Swift class that inherits from NSObject and you implement the == operator.
You don't automatically get the != operator from the standard library, as stated in the documentation.

class TestClass: NSObject { }
func ==(lhs: TestClass, rhs: TestClass) -> Bool {
    return true
}

let a = TestClass()
let b = TestClass()

a == b // TestClass implementation of == gets called
a != b // Doesn't call TestClass implementation of == and return the inverse. Instead it calls the isEqual function.
@belkadan
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This is correct behavior. NSObject's implementation of == calls isEqual, and it's NSObject's implementation that's used to conform to Equatable. != is defined in terms of Equatable, so it's always going to use that one.

If you want to customize equality for a subclass of NSObject, you have to use NSObject's designated override point for customizing equality, isEqual.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior.
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@belkadan @swift-ci