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[SR-2139] 'let' ivars in generic subclass of NSObject invalid #44747

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swift-ci opened this issue Jul 21, 2016 · 4 comments
Closed

[SR-2139] 'let' ivars in generic subclass of NSObject invalid #44747

swift-ci opened this issue Jul 21, 2016 · 4 comments
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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 3.0

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@swift-ci
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Previous ID SR-2139
Radar rdar://problem/27495735
Original Reporter mattgallagher (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

Version 8.0 beta 3 (8S174q)

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, 3.0Regression
Assignee None
Priority Medium

md5: 4bbf8b4677cba6abe7fe12f3e7f55197

Issue Description:

The following code should print "5" but prints "0" in Swift 3 (both -O and -Onone)

Code works as expected in Swift 2.3.

import Foundation

class Box<T>: NSObject {
    let value: T
    init(_ t: T) {
        value = t
    }
}

let b = Box(5)
print(b.value)

Any of the following will work around the problem: don't inherit from NSObject, replace generic parameter with `Int`, replace `let` with `var`.

According to debugger, correct value is passed into constructor and assigned to `value`. Problem appears to occur after that point.
@belkadan
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Yikes. @jckarter, @slavapestov, any ideas?

@swift-ci
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Comment by Matt Gallagher (JIRA)

In the latest beta (Xcode beta 5) this problem does not always occur. Roughly 30% of the time, going around in a: clean project -> build -> run, the result is 0 and 70% of the time it's 5. Something dirty happening.

@belkadan
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belkadan commented Aug 1, 2017

Whatever this was, we seem to have fixed it. I suspect it was Slava's work fixing instance variable offsets for generic subclasses of Objective-C classes.

@swift-ci
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swift-ci commented Aug 2, 2017

Comment by Matt Gallagher (JIRA)

Just adding confirmation that this appears to be fixed. Sorry I didn't revisit this myself... it appears to be fixed since Xcode 8.3.

@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. compiler The Swift compiler in itself regression swift 3.0
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@belkadan @swift-ci @AnthonyLatsis