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<body><div>Any thoughts on instead having to mark the default method implementations as `default`?<br></div>
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<div>It still seems strange to me to consider a protocol extension that uses the `final` keyword, because a) protocols have nothing to do with classes and `final` means no subclassing, and b) methods defined in protocol extensions by definition can't be overridden already, so the `final` keyword is just sort of like saying "no really, I mean it, you can't do the thing you already can't do!". But since I see the value in making it clear which methods are default implementations (and thus can be overridden), and which are actually just new methods, I'm in favor of using the `default` keyword on the former:<br></div>
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<div><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;">protocol Foo {</span><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"><br></span></div>
<div><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"> func foo() -> String</span><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"><br></span></div>
<div><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;">}</span><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"><br></span></div>
<div> </div>
<div><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;">extension Foo {</span><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"><br></span></div>
<div><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"> default func foo() -> String { return "foo!" }</span><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"><br></span></div>
<div><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"> func bar() -> String { return "bar" }</span><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"><br></span></div>
<div><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;">}</span><span class="font" style="font-family: menlo, consolas, "courier new", monospace, sans-serif;"><br></span></div>
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<div>-Kevin</div>
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<div>On Wed, Dec 9, 2015, at 09:37 AM, thorsten--- via swift-evolution wrote:<br></div>
<blockquote type="cite"><div> </div>
<div>This won't work if the protocol is provided by someone else (meaning I can't change its source code) and I want to provide a protocol extension in my own module.<br></div>
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<div>I like the original idea of having to mark extension methods not in the protocol definition as final. This would make the semantics much clearer.<br></div>
<div> </div>
<div>-Thorsten<br></div>
<div><div> </div>
<div>Am 09.12.2015 um 11:22 schrieb T.J. Usiyan via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>:<br></div>
</div>
<blockquote type="cite"><div><div dir="ltr"><div>I actually suggest something along the lines of <br></div>
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<div><div><span class="size" style="font-size:13px"> protocol Foo {</span><br></div>
<div><span class="size" style="font-size:13px"> final func doIt() -> String</span><br></div>
<div><span class="size" style="font-size:13px"> }</span><br></div>
</div>
<div> </div>
<div><span class="size" style="font-size:13px"> extension Foo {</span><br></div>
<div><span class="size" style="font-size:13px"> final func doIt() -> String {</span><br></div>
<div><span class="size" style="font-size:13px"> print("I did it.")</span><br></div>
<div><span class="size" style="font-size:13px"> }</span><br></div>
<div><span class="size" style="font-size:13px"> final </span>func doThat() {<br></div>
<div> print("I did that.")<br></div>
<div> }<br></div>
<div><span class="size" style="font-size:13px"> }</span><br></div>
<div> </div>
<div>to indicate that foo will be provided in this module and is not ever to be dynamically dispatched. This draws attention to the fact that dispatch is static in a clear consistent manner.<br></div>
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<div>TJ<br></div>
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<div><div> </div>
<div><div>On Wed, Dec 9, 2015 at 1:31 PM, Gwendal Roué <span dir="ltr"><<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>></span> wrote:<br></div>
<blockquote style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0.8ex;border-left-width:1px;border-left-color:rgb(204, 204, 204);border-left-style:solid;padding-left:1ex;"><div><span><br>
> Le 9 déc. 2015 à 06:31, Paul Cantrell <<a href="mailto:cantrell@pobox.com">cantrell@pobox.com</a>> a écrit :<br>
><br>
> Gwendal Roué wrote:<br>
>> Whatever the direction this proposal is aiming at, please remember that it is desirable for some APIs to let adopting types "override" the default implementation provided by protocols.<br>
><br>
><br>
> I would certainly hope nobody is proposing changing that! Once a method is virtually dispatched, it should be virtual all the way down to the implementing type.<br> <br></span>Yes, and it’s why I’m concerned. When a protocol provides a default implementation, how will an adopting type invoke that default implementation in its own implementation?</div>
<div> </div>
<div>
With classes, it’s easy: you call super.<br></div>
<div> </div>
<div>
With protocols, it’s much less easy, if possible at all, as soon as all methods are dynamically dispatched.<br></div>
<div><div><div> </div>
<div>
Gwendal Roué<br></div>
<div> </div>
<div> </div>
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