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[SR-6165] Overriding computed property with stored one is not allowed unless it is lazy #48717

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swift-ci opened this issue Oct 16, 2017 · 2 comments
Closed

[SR-6165] Overriding computed property with stored one is not allowed unless it is lazy #48717

swift-ci opened this issue Oct 16, 2017 · 2 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself

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@swift-ci
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Previous ID SR-6165
Radar None
Original Reporter frangulyan (JIRA User)
Type Bug
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug
Assignee None
Priority Medium

md5: 301431c66b14d31c641d261286db7903

relates to:

  • SR-6980 Swift 4.1 new warning "Cannot override with a stored property"

Issue Description:

Given classes A and B like this:

class A {
    var x: Int { return 9 }
    func p() {  print(x) }
}

class B: A {
    ...
}

let v: A = B()
v.p()

overriding x in B in three different ways have the following results:

class B: A {
    // OPTION 1: FINE - prints 10
    override var x: Int { return 10 }

    // OPTION 2: ERROR - cannot override with a stored property 'x'
    override var x = 10

    // OPTION 3: FINE - prints 10
    override lazy var x = 10
}

As suggested in this answer there are cases in which overriding seems to be possible to be done without giving an error.
@belkadan
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Oh, cute—a lazy property is implemented behind the scenes as computed, so it sneaks past the check. Fixing that would break source compatibility at this point.

Thanks for finding this.

@belkadan
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"Fixed" in #13304 and #13335 You now get a warning in Swift 3/4 and an error in Swift 5.

@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. compiler The Swift compiler in itself
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@belkadan @swift-ci