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[SR-1271] Protocol extension method being called over subclass implementation. #43879

swift-ci opened this issue Apr 20, 2016 · 1 comment


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@swift-ci swift-ci commented Apr 20, 2016

Previous ID SR-1271
Radar None
Original Reporter dlbuckley (JIRA User)
Type Bug
Status Resolved
Resolution Duplicate

Attachment: Download


Xcode 7.3, Swift 2.2, OSX 10.11.4

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

md5: 606381dd1b70783cd53f6d0bee513f00


  • SR-103 Protocol Extension: function's implementation cannot be overridden by a subclass
  • SR-118 Protocol extensions cannot be overridden in subclasses

Issue Description:

I have come across an issue where I want to have a class conform to a protocol by default, but the protocol has default implementations of all it's methods through an extension. I then want to subclass the original class and optionally implement the protocol methods.

Unfortunately by trying to do this I ran into a problem where the methods in the protocol extension were being called over the methods implemented in the subclass which I believe is unintended behaviour. The methods implemented in the main class were being called instead of the protocol extension methods fine.

I have included a Xcode playground to demonstrate this behaviour.

protocol MyProtocol {
    func doTheFirstThing()
    func doTheSecondThing()
    func doTheThirdThing()

extension MyProtocol {
    func doTheFirstThing() {
        print("The DEFAULT first thing")
    func doTheSecondThing() {
        print("The DEFAULT second thing")
    func doTheThirdThing() {
        print("The DEFAULT third thing")

class MyClass: MyProtocol {
    func myMethod() {
    func doTheFirstThing() {
        print("This implementation of the first thing should be called instead of the default implementation")

class MySubclass: MyClass {
    func doTheSecondThing() {
        print("This implementation of the second thing should be called instead of the default implementation")

// This implementation of the first thing should be called instead of the default implementation
// The DEFAULT second thing (This should be the implementation from the subclass)
// The DEFAULT third thing
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@swift-ci swift-ci commented Apr 20, 2016

Comment by Dale Buckley (JIRA)

After having a search around I've found this is a duplicate of SR-118, but according to that ticket it was resolved on 8th December 2015. As it stands that was several months before Swift 2.2 so I would assume that it would be included in that release, but this is not the case.

I don't know where to track this particular fix in the codebase as there are no references to releases in the resolved issue. I will link this open issue to it as a duplicate, but it's an ongoing issue that has yet to be resolved.

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