[swift-evolution] [Discussion] Protocol member deprecations

[Charlie Monroe]

I am currently working on updating some protocol APIs in a framework that's shared among several of my projects. The issue here is that the protocol has an extension with default implementation. For example:

protocol Foo {
    func doSomethingWithArray(_ arr: [String])
}

extension Foo {
    func doSomethingWithArray(_ arr: [String]) {
        print(arr)
    }
}

With this you can easily write 

struct Bar: Foo { }


The issue comes when the struct actually implements the method and you decide to rename it in the protocol:

struct Bar: Foo {
    func doSomethingWithArray(_ arr: [String]) {
        fatalError()
    }
}


protocol Foo {
    func doSomething(with arr: [String])
}

extension Foo {
    func doSomething(with arr: [String]) {
        print(arr)
    }
}

The code still compiles, yet the behavior of the app changes incredibly. There is no way (to my knowledge) of marking some protocol members as deprecated. I've tried the "obvious" solution:

extension Foo {
    @available(*, deprecated, renamed: "doSomething(with:)")
    func doSomethingWithArray(_ arr: [String]) {
        self.doSomething(with: arr)
    }
}

But unfortunately, this doesn't emit any warning on the Bar structure. I personally believe that this is a major flaw, given that Swift is being claimed as Protocol-Oriented language, there is no way to declare that a protocol method is deprecated/renamed. Mainly with protocols with default implementations (or in ObjC optional).

I know there were discussions about marking members that should implement the protocol requirements with a keyword, but unfortunately, most members here were against such a proposal as it would introduce a lot of visual clutter.

I'm suggesting that implementing a same-named member from a protocol marked as "deprecated" that also has a default implementation would emit a warning.

Does anyone else view this as an issue in the language?




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170204/878af5ac/attachment.html>