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[SR-9052] Cannot access protocol property returning Self on an existential #51555

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hamishknight opened this issue Oct 20, 2018 · 0 comments
Open

[SR-9052] Cannot access protocol property returning Self on an existential #51555

hamishknight opened this issue Oct 20, 2018 · 0 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis

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@hamishknight
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Previous ID SR-9052
Radar None
Original Reporter @hamishknight
Type Bug
Environment

Swift version 4.2-dev (LLVM c4a0883115, Clang 0a99881462, Swift 533575ab62)
Target: x86_64-apple-darwin17.7.0

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

md5: 96ac2f701281716b3ac14ff121110227

Issue Description:

The following doesn't compile:

protocol P {}
extension P {
  var foo: Self { return self }
}

func bar(_ x: P) {
  let y = x.foo // error: Member 'foo' cannot be used on value of protocol type 'P'; use a generic constraint instead
}

But really it ought to compile – we should erase Self back to P, just like we do with methods and subscripts:

protocol P {}
extension P {
  func foo() -> Self { return self }
  subscript(foo: String) -> Self { return self }
}

func bar(_ x: P) {
  let y = x.foo() // fine
  let z = x[""] // also fine
}
@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis
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@hamishknight