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[SR-11488] Implicit inout allowed with expression pattern matching #53888

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hamishknight opened this issue Sep 19, 2019 · 3 comments
Open

[SR-11488] Implicit inout allowed with expression pattern matching #53888

hamishknight opened this issue Sep 19, 2019 · 3 comments
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@theblixguy
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis

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@hamishknight
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Previous ID SR-11488
Radar None
Original Reporter @hamishknight
Type Bug
Status In Progress
Resolution
Environment

Swift version 5.1-dev (LLVM c5340df2d1, Swift 0cbbb21723)
Target: x86_64-apple-darwin18.5.0

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

md5: 1c04b5748355a33fd8b2071e29f6d302

Issue Description:

The following is legal:

func ~= (pattern: inout Int, value: Int) -> Bool {
  pattern = value
  return true
}

var x = 0

switch 49 {
case x:
  print("yup")
default:
  print("nope")
}

print(x) // 49

But we probably shouldn't allow the pattern x to be used as an implicit inout argument. This is source breaking, but I would hope nobody is relying on this.
@belkadan
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Yuck. @jckarter, as a core team member, you want to say that this is an acceptable source break?

@jckarter
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Yeah, I think that's clearly a bug.

@theblixguy
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PR: #27332

I have also created a thread on swift-evolution to decide whether we should:

  1. Skip ~= functions that take the pattern inout

  2. Diagnose ~= functions with a fix-it to remove inout

The current implementation does (1) because its simpler, but I can update it to do (2) instead if that's preferable.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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@theblixguy theblixguy

Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself type checker Area → compiler: Semantic analysis
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4 participants
@jckarter @belkadan @theblixguy @hamishknight