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[SR-5876] Swift 4 no longer infers inout parameters #48446

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lilyball mannequin opened this issue Sep 12, 2017 · 3 comments
Closed

[SR-5876] Swift 4 no longer infers inout parameters #48446

lilyball mannequin opened this issue Sep 12, 2017 · 3 comments
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@xedin
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression swift 4.0 type checker Area → compiler: Semantic analysis

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@lilyball
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Mannequin

lilyball mannequin commented Sep 12, 2017

Previous ID SR-5876
Radar None
Original Reporter @lilyball
Type Bug
Status Closed
Resolution Done
Environment

Xcode 9.0 (9A235)

Apple Swift version 4.0 (swiftlang-900.0.65 clang-900.0.37)
Target: x86_64-apple-macosx10.9

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, 4.0Regression, TypeChecker
Assignee @xedin
Priority Medium

md5: eede21d4c9a5d30d1daac160c51a12fd

Issue Description:

Swift 3.1 infers inout parameters correctly. For example:

let seq = sequence(state: 1 as Int, next: { (counter) -> Int? in
    defer { counter += 1 }
    return counter == 10 ? nil : counter
})
print(seq.reduce(0, +))

This correctly compiles and prints 45. But Swift 4 complains instead with the error

unnamed.swift:2:21: error: left side of mutating operator isn't mutable: 'counter' is a 'let' constant
    defer { counter += 1 }
            ~~~~~~~ ^
@belkadan
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@xedin, is this what you were just looking at recently?

@xedin
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xedin commented Sep 13, 2017

Thanks, @belkadan! Yes, this has been fixed by #11855 which prevents invalid contractions of subtype constraints.

Eridius (JIRA User) please use the latest nightly build of the compiler to verify.

@lilyball
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lilyball mannequin commented Sep 14, 2017

Verified, the latest nightly compiles this code correctly.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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@xedin xedin

Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression swift 4.0 type checker Area → compiler: Semantic analysis
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@xedin @belkadan @AnthonyLatsis