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

[jeremyabannister]

Previous ID	SR-8805
Radar	None
Original Reporter	@jeremyabannister
Type	Bug
Status	Resolved
Resolution	Duplicate

Additional Detail from JIRA

Votes	0
Component/s
Labels	Bug
Assignee	None
Priority	Medium

md5: a287be58d0bdbdb7b069381c1a1f5ce1

duplicates:

• 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
}

[belkadan]

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