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[SR-7664] Inconsistent optional casting behaviour with generics #50204

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hamishknight opened this issue May 11, 2018 · 4 comments
Closed

[SR-7664] Inconsistent optional casting behaviour with generics #50204

hamishknight opened this issue May 11, 2018 · 4 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself

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@hamishknight
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Previous ID SR-7664
Radar rdar://problem/40171034
Original Reporter @hamishknight
Type Bug
Status Resolved
Resolution Done
Environment

Swift version 4.2-dev (LLVM d9cd6a5c49, Clang ed8876508e, Swift c363dad)
Target: x86_64-apple-darwin17.5.0

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

md5: 241ea289c2d537b07e80e0f58cf55573

is duplicated by:

  • SR-8037 Method generic type inference is broken in Swift 4.2

Issue Description:

This cast succeeds:

func foo(_ t: Int??) -> Int? {
  return t as? Int
}
let x = foo(Int??(3))
print(x as Any) // Optional(3)

but it fails when we use a generic placeholder satisfied by Int rather than Int directly. This cast fails:

func bar<U>(_ t: Int??, _: U.Type) -> U? {
  return t as? U
}

let y = bar(Int??(3), Int.self)
print(y as Any) // nil
@belkadan
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@rudkx, you were looking at some of this, right?

@belkadan
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@swift-ci create

@rudkx
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rudkx commented May 11, 2018

I was looking at something a little different than this that did not involve generics.

This seems like it must be an issue with the conditional casting support in the runtime.

@mikeash
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mikeash commented May 22, 2018

Fixed in this PR: #16772

@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. compiler The Swift compiler in itself
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4 participants
@rudkx @mikeash @belkadan @hamishknight