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[SR-1466] Collection.Indices doesn't expose Comparable elements #44075

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glessard opened this issue May 10, 2016 · 4 comments
Closed

[SR-1466] Collection.Indices doesn't expose Comparable elements #44075

glessard opened this issue May 10, 2016 · 4 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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@glessard
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Previous ID SR-1466
Radar None
Original Reporter @glessard
Type Bug
Status Closed
Resolution Done
Environment

Apple Swift version 3.0-dev (LLVM dffa09ffd8, Clang 9f0d189820, Swift 1c720b8)
(on OS X)

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

md5: f99df57548a484701b7b53e48286a839

Issue Description:

Comparable is a requirement of Collection.Index, yet the Sequence returned by Collection.Indices hides that its element type conforms to Comparable.

func f<C: Collection>(c: C) {
  let s = c.startIndex
  for i in c.indices {
    if s == i { break }
    // Argument type 'C.Indices.Iterator.Element' does not conform to expected type 'Comparable'
  }
}

I can restrict the generic parameter thusly:

func g<C: Collection where C.Indices.Iterator.Element == C.Index>(c: C) {
  let s = c.startIndex
  for i in c.indices {
    if s == i { break } // no problem
  }
}

It seems this should always be true.
@glessard
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Even less useful:

func function<C: Collection>(c: C) {
  for index in c.indices {
    _ = c[index] // Cannot subscript a value of type 'C' with an index of type 'C.Indices.Iterator.Element'
  }
}

@Dante-Broggi
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I think this would have been fixed in Swift 4.2, with SE-0143 (Conditional Conformances).

@glessard
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It was actually fixed as far back as Swift 4.0.2. Thanks for the reminder.

@glessard
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Fixed in Swift 4.0.2

@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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@glessard @Dante-Broggi