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[SR-8595] Protocol extension on protocol with subclass where restriction doesn't apply : class semantics #51111

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zwaldowski opened this issue Aug 21, 2018 · 1 comment
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[SR-8595] Protocol extension on protocol with subclass where restriction doesn't apply : class semantics #51111

zwaldowski opened this issue Aug 21, 2018 · 1 comment
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior.

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@zwaldowski
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Previous ID SR-8595
Radar None
Original Reporter @zwaldowski
Type Bug
Status Resolved
Resolution Duplicate
Environment

Xcode Version 10.0 beta 6 (10L232m), Apple Swift version 4.2 (swiftlang-1000.0.36 clang-1000.10.44)

(Also occurs in Swift 4.1.x)

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

md5: a35b960b5edfe17ce447790f7be32d57

duplicates:

  • SR-5581 Proper support for protocol 'where' clause with constraints on 'Self'

Issue Description:

Consider a protocol with a class constraint: protocol Fooable: class

I can add a protocol extension to Fooable with a property that has a setter, and use the setter on with reference semantics. let x = MyClass(); x.bar = "qux"

Now consider adding a where constraint to the protocol: protocol Fooable where Self: UIViewController.

I am warned that marking the protocol `: class`, is redundant ("Redundant constraint" 'Self': 'AnyObject"), however, if I remove it I can no longer use the setter above with reference semantics ("Cannot assign to property: 'vc' is a 'let' constant"). If I ignore the warning, the original code still works.
@zwaldowski
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Additionally, you can't have a weak var despite the constraint. I imagine that's the same issue, but can file it separately if it seems not.

@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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@zwaldowski