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[SR-10775] Mutating method in protocol extension always requires variable to be var #53165

swift-ci opened this issue May 26, 2019 · 0 comments


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swift-ci commented May 26, 2019

Previous ID SR-10775
Radar None
Original Reporter fumoboy007 (JIRA User)
Type Bug
Status Closed
Resolution Duplicate

Attachment: Download


Apple Swift version 5.0.1 (swiftlang-1001.0.82.4 clang-1001.0.46.5)
Target: x86_64-apple-darwin18.6.0

Additional Detail from JIRA
Votes 0
Labels Bug
Assignee None
Priority Medium

md5: ab0a323b49b55ccc543bf96676de562c


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

Issue Description:

Consider the following code:

protocol ProtocolWithMutableMethod {
   mutating func mutateStuff()

extension ProtocolWithMutableMethod {
   mutating func mutateStuff() {

struct MyClass: ProtocolWithMutableMethod {

let object = MyClass()

The compiler complains “Cannot use mutating member on immutable value: 'object' is a 'let’ constant” even though object is clearly a reference type where everything is mutable.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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