[swift-evolution] [Proposal] Revising access modifiers on extensions

[Adrian Zubarev]

“The access modifier of an extension sets the default modifier of its members which has no modifier applied to them.”
public extension SomeType {
    func extensionMember() {}
}
“If there the extension has no access modifier, then the default modifier of its members which has no explicit modifier will be internal if the extended type is either public or internal, or it will be private when the extended type is private(analogous for fileprivate).”
// First
public/internal struct A {}

extension A {
     
    /* internal */ func member() {}
}

// Second
private struct B {}

extension B {
     
    /* private */ func member() {}
}
My English isn’t great, please don’t blame me for that. Feel free to correct me. I’d appreciate that. :)

But more importantly, I was under the impression that Doug had hinted that private (or likely more generally scoped) conformance on extension was a slipery slope with important impact on runtime performance.
I’m not an expert in this area, I really cannot tell. And I don’t want to dig in all these thousands of emails to find his talk. FWIW not every proposal does know the impact which will happen behind the scene. Even some simple change might have a huge impact (I don’t say this proposal is simple).

My personal vision of the access control is clarity and consistency. It would be much easier to have the same access control behavior on extensions like on classes, enums and structs.


-- 
Adrian Zubarev
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