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[SR-11511] A returning value of Array<Void> should give a warning, like Optional<Void> #53912

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BasThomas opened this issue Sep 24, 2019 · 7 comments
Closed

[SR-11511] A returning value of Array<Void> should give a warning, like Optional<Void> #53912

BasThomas opened this issue Sep 24, 2019 · 7 comments
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compiler The Swift compiler in itself good first issue Good for newcomers improvement

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@BasThomas
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Previous ID SR-11511
Radar None
Original Reporter @BasThomas
Type Improvement
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Improvement, StarterBug
Assignee jder (JIRA)
Priority Medium

md5: ebcfa84ec27da83a255c80a10ed317da

Issue Description:

let optOne: Int? = 1
let y = optOne.map { _ in return () } // Constant 'y' inferred to have type '()?', which may be unexpected
let z = [""].map { _ in return () } // no warning.

// The expected warning would be:
// Constant 'z' inferred to have type '[()]', which may be unexpected

For more information see the thread in this tweet.
@belkadan
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@xedin, @hborla, what do you think? Helpful or not worth it? Also, starter-bug-able or not?

@theblixguy
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Yeah, it's starter-bug worthy. We need to add another check here to account for an ArraySliceType with Void as base type.

@ZevEisenberg
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Should it also give a suggestion, like putting an extra set of parentheses or writing Void explicitly to silence the warning? Or is there no reasonable case where you would actually intend to do this?

@theblixguy
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I think there should be a fix-it to insert an explicit type annotation, I can’t remember if we do it for the Optional<Void> case as well.

@belkadan
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Looks like we don't today but we totally should.

<stdin>:2:5: warning: constant 'y' inferred to have type '()?', which may be unexpected
let y = x.map { print($0) }
    ^
<stdin>:2:5: note: add an explicit type annotation to silence this warning
let y = x.map { print($0) }
    ^

@swift-ci
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Comment by Jesse Rusak (JIRA)

I made a quick PR for these two ideas here #27797

Feedback very welcome!

@swift-ci
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Comment by Jesse Rusak (JIRA)

PR is now merged.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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compiler The Swift compiler in itself good first issue Good for newcomers improvement
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@ZevEisenberg @belkadan @theblixguy @BasThomas @swift-ci