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[SR-13847] Wrong generic used in extensions #56245

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swift-ci opened this issue Nov 12, 2020 · 2 comments
Open

[SR-13847] Wrong generic used in extensions #56245

swift-ci opened this issue Nov 12, 2020 · 2 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior.

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@swift-ci
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Previous ID SR-13847
Radar rdar://problem/71330233
Original Reporter David2X (JIRA User)
Type Bug
Additional Detail from JIRA
Votes 0
Component/s
Labels Bug
Assignee None
Priority Medium

md5: 1db7e674f8f1fcaff55a47d1eb4e85a0

Issue Description:

For some reason when calling initializer in extension, compiler tries to match unrelated generics.

Example with Array:
✔ Works in function:

func enumeratedWithIndex(array: [Int]) {
    let zipped = zip(array.indices, array)
    let ret = Array(zipped)
}

❌ Does not work in extension

extension Array where Element == Int {
    func enumeratedWithIndex() /*-> [(Int, Element)]*/ {
        let array = self
        let zipped = zip(array.indices, array)
        let ret = Array(zipped)
    }
}

Error on line

let ret = Array(zipped)
Initializer 'init(_:)' requires the types 'Int' and 'Zip2Sequence<Range<Array<Int>.Index>, [Int]>.Element' (aka '(Int, Int)') be equivalent

💡 The only workaround is to manually specify generics:

extension Array where Element == Int {
    func enumeratedWithIndex() /*-> [(Int, Element)]*/ {
        let array = self
        let zipped = zip(array.indices, array)
        let ret = Array<(Int,Int)>(zipped)
    }
}
@typesanitizer
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Doesn't seem to be specific to array. Reduced:

struct S<T> { let t: T }
extension S where T == Int {
  func f() {
    let s1 = S(t:1) // OK
    let s2 = S(t:"X") // error: cannot convert value of type 'String' to expected argument type 'Int'
  }
}

@typesanitizer
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@swift-ci create

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior.
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@typesanitizer @swift-ci