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[SR-2559] EXC_BAD_ACCESS when comparing two optionals #45164

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swift-ci opened this issue Sep 4, 2016 · 7 comments
Closed

[SR-2559] EXC_BAD_ACCESS when comparing two optionals #45164

swift-ci opened this issue Sep 4, 2016 · 7 comments
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@CodaFi
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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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swift-ci commented Sep 4, 2016

Previous ID SR-2559
Radar None
Original Reporter simplgy (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

Version 8.0 beta 5 (8S193k)

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

md5: 3347db583ab3a5058e6686a7c2f8a53b

relates to:

  • SR-626 No diagnostic for unconditional recursion

Issue Description:

I have a reproducible crash in playground environment.
The formatting here is bad, so you can see the code here: https://gist.github.com/SimplGy/934af7b6bd43b1296a4fa168fd2137bc

Or it is below for completeness.

No Runtime Error:

func == (l: Car, r: Car) -> Bool { return l.vin == r.vin }
struct Car { let vin: String }
protocol hasDriversLicense: class {
  var car: Car? { get set }
}
class YoungPro: hasDriversLicense {
  var car: Car? { didSet {
    if let oldValue = oldValue, car = car, oldValue == car { return }
    print("car changed")
  }}
  init(){}
}
let you = YoungPro()
you.car = Car(vin: "abc123")

Runtime error:

func == (l: Car?, r: Car?) -> Bool {
  if l == nil && r == nil { return true }
  guard let l = l, let r = r else { return false }
  return l.vin == r.vin
}
struct Car { let vin: String } // class, struct, tuple... doesn't matter

protocol hasDriversLicense: class {
  var car: Car? { get set }
}

class YoungPro: hasDriversLicense {
  var car: Car? { didSet {
    if oldValue == car { return }
    print("car changed")
  }}
  init(){}
}

let you = YoungPro()
you.car = Car(vin: "abc123") // EXC_BAD_ACCESS code: 2
@belkadan
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belkadan commented Sep 6, 2016

The == nil is just calling the same function over again, rather than using the == in the standard library for comparing to nil. I'm not sure I'd even call this incorrect behavior, but it certainly isn't useful. @rudkx, what do you think?

@swift-ci
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swift-ci commented Sep 7, 2016

Comment by Eric (JIRA)

Oh! Of course. I'm sure there's a way to check for nil without using `== nil` but that didn't even occur to me.

@belkadan
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belkadan commented Sep 7, 2016

A related enhancement request here would be something like Clang's -Winfinite-recursion: we have a call to the containing function here that happens on all paths.

@belkadan
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belkadan commented Sep 7, 2016

You can check for nil by using if case nil = l, or by using a switch. Both of those are a little uglier, though, so I still wonder if we should come up with a better answer.

@rudkx
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rudkx commented Sep 12, 2016

Generally the "right" way to implement this is to make Car conform to Equatable, define the "func ==" for Cars, and then for optionals let the generic form of "func ==" for optionals of Equatables kick in.

I think a warning like -Winfinite-recursion would be a fine idea, though.

@swift-ci
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Comment by Eric (JIRA)

Yeah, that would work great Mark. I stumbled on this because I was trying to implement this for a `typealias` on a tuple, so I (didn't think I could) make it conform to Equatable. Didn't want to include that complexity in the example though.

@CodaFi
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CodaFi commented Feb 27, 2018

Resolved by the merge of #11869.

@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
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@rudkx @belkadan @CodaFi @swift-ci