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[SR-5551] Keypath of implicitly unwrapped optional #48123

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swift-ci opened this issue Jul 25, 2017 · 7 comments
Closed

[SR-5551] Keypath of implicitly unwrapped optional #48123

swift-ci opened this issue Jul 25, 2017 · 7 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation

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@swift-ci
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Previous ID SR-5551
Radar rdar://problem/33525846
Original Reporter cuva (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

Swift 4

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

md5: 807f5fda1f3703ae233a77354933c497

Issue Description:

We're unable to pass a key path referencing an implicitly unwrapped optional object to a function as:

let keyPath = \UIView.tintColor // ReferenceWritableKeyPath<UIView, UIColor!>

func doSomething(using keyPath: ReferenceWritableKeyPath<UIView, UIColor!>) {
  [...]
}

Fails with the following build error:

error: implicitly unwrapped optionals are only allowed at top level and as function results
func doSomething(using keyPath: ReferenceWritableKeyPath<UIView, UIColor!>)

Is this a known issue?

Should key path of implicitly unwrapped optionals be mapped to optionals?
@belkadan
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@jckarter, did your work on regular Optionals fix this?

@jckarter
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The error is correct, to the letter of SE-0054 at least, though we have lots of known issues with the implementation. `T!` is in theory an attribute that only applies to certain declarations and becomes plain `T?` once you bring it into arbitrary type position. ReferenceWritableKeyPath<UIView, UIColor?> ought to work.

@belkadan
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Oops, I completely glanced past the actual text of the message. Maybe we can change the diagnostic here to suggest using Optional instead.

@belkadan
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Ah, but the implicit type of the key path has the IUO in it. That's a key-path-specific bug.

let keyPath = \UIView.tintColor
let x: Int = keyPath

error: cannot convert value of type 'ReferenceWritableKeyPath<UIView, UIColor!>' to specified type 'Int'

@jckarter
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Well, it's a systemic problem with the type checker still handling IUO as a first-class type. This isn't the only place it manifests.

@jckarter
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@swift-ci create

@rjmccall
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This has been fixed now that we don't treat IUO as a separate type. We give a fixit to use ? instead of !, and ? causes the code to compile.

@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 diagnostics QoI Bug: Diagnostics Quality of Implementation
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@jckarter @belkadan @rjmccall @swift-ci