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[SR-8805] Cannot set protocol extension property on adopting reference type which is immutable #51313

jeremyabannister opened this issue Sep 20, 2018 · 1 comment


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jeremyabannister commented Sep 20, 2018

Previous ID SR-8805
Radar None
Original Reporter @jeremyabannister
Type Bug
Status Resolved
Resolution Duplicate
Additional Detail from JIRA
Votes 0
Labels Bug
Assignee None
Priority Medium

md5: a287be58d0bdbdb7b069381c1a1f5ce1


  • SR-142 mutating function in protocol extension erroneously requires var declaration of class variables

Issue Description:

I really hate to waste the Swift team's time and distract you from more important things, so if this issue is an intentional restriction of the language then please feel free to archive this "bug" and not respond in any way. Here is the code which doesn't compile even though I wish it did:

protocol A {
  var a: Int { get set }

extension A {
  var convenientAccessor: Int {
    get { return a }
    set { a = newValue }

class B: A {
  var a: Int = 0

func acceptsB (instance: B) {
  instance.a = 1                    // This compiles
  instance.convenientAccessor = 2   // This does not
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belkadan commented Sep 20, 2018

It's not a bug, but it is confusing. Check out the explanation in SR-142.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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