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[SR-7239] Optional(nil) ? #49787

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swift-ci opened this issue Mar 20, 2018 · 2 comments
Closed

[SR-7239] Optional(nil) ? #49787

swift-ci opened this issue Mar 20, 2018 · 2 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella

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@swift-ci
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Previous ID SR-7239
Radar None
Original Reporter mshibanami (JIRA User)
Type Bug
Status Resolved
Resolution Invalid

Attachment: Download

Environment

Apple Swift version 4.1 (swiftlang-902.0.43 clang-902.0.37.1)
Target: x86_64-apple-darwin17.4.0

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

md5: 15dc48b497ed49c70364a0b2f8640840

Issue Description:

See this code:

extension Array {
    func func1() {
        var optionals: [Element?] = self
        optionals[0] = self[0]
        print(optionals)

        let nonnulls
            = optionals.compactMap { $0 }
    }
}
[nil,1,2].func1()

  • I thought the nonnulls will be [1,2]. but actual value was [nil, 1, 2]. compactMap() didn't remove the nil.

  • print(optionals) outputs "[Optional(nil), Optional(Optional(1)), Optional(Optional(2))]"

Is this the expected result?
To be honest, I'm not sure this is a bug or a specification.
@belkadan
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This is correct behavior; it's okay for Optionals to contain other Optionals, and so when you run this function you end up with [Int??], not just [Int?]. Then compactMap takes out all the top-level nil values, but not Optional(nil).

@swift-ci
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Comment by Manabu Nakazawa (JIRA)

Oh, I see. I didn't know about `??`.

This was a newbie issue. Sorry.

And thank you for letting me know!

@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. standard library Area: Standard library umbrella
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@belkadan @swift-ci