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[SR-2498] Foo.self is AnyObject incorrectly claims it always returns true #45103

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lilyball mannequin opened this issue Aug 27, 2016 · 2 comments
Closed

[SR-2498] Foo.self is AnyObject incorrectly claims it always returns true #45103

lilyball mannequin opened this issue Aug 27, 2016 · 2 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior.

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@lilyball
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Mannequin

lilyball mannequin commented Aug 27, 2016

Previous ID SR-2498
Radar None
Original Reporter @lilyball
Type Bug
Status Resolved
Resolution Duplicate
Environment

Apple Swift version 3.0 (swiftlang-800.0.43.6 clang-800.0.38)
Target: x86_64-apple-macosx10.9

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

md5: 2451fc1637b9025dc20c2e0c5fb85bd0

duplicates:

  • SR-2420 AnyObject not working in Xcode8 beta6

Issue Description:

With Xcode 8 beta 6, if I write Foo.self is AnyObject, where Foo is a generic parameter or is something known to be a value type (e.g. a struct), the compiler warns me warning: 'is' test is always true, but at runtime it evaluates to false.

struct Foo {
    var x: Double
    var y: Double
}

print(Foo.self is AnyObject)

Compiler output:

unnamed.swift:6:16: warning: 'is' test is always true
print(Foo.self is AnyObject)
               ^

Runtime output:

false
@lilyball
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Mannequin Author

lilyball mannequin commented Aug 27, 2016

FWIW I think the error here is the warning, not the runtime behavior. My use-case here is explicitly trying to check if a generic parameter is an object type. I don't want to invoke the new automatic value-type boxing behavior.

@lilyball
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lilyball mannequin commented Aug 27, 2016

Hmm, after some quick experimentation, it looks like saying Foo.self is AnyObject.Type actually does what I want with no warning. So I guess I'm not sure how Foo.self is AnyObject should actually behave (but however it behaves, the compiler warning and runtime behavior need to be consistent).

@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.
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