<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Aug 25, 2016, at 4:32 PM, Christopher Kornher <<a href="mailto:ckornher@me.com" class="">ckornher@me.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">I hope that my brief email wasn’t the final word on this :(</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">Does anyone think that a proposal to require “override” for overrides of protocol extension methods and variables (?) would be worth exploring?</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">This would address a number of the issues raised in this thread, but not all.</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">My intention is not to derail this thread, and I believe that the original topic of this thread, explicit protocol conformance, is worth exploring. I respond here because of these topics are strongly related. I will start a new thread, if there is interest.</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">It is possible that tooling could address the remaining issues with overrides. JetBrains products, for example, provide navigable icons to overridden methods. There is no reason that Xcode and other tools could not automatically insert indicators like:</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">```</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">class MyClass: MyProtocol {</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>< conforms ></span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func myMethod() -> String {</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""> <span class="Apple-tab-span" style="white-space:pre"> </span>return “..."</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""> <span class="Apple-tab-span" style="white-space:pre"> </span>}</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">class MyClass2: MyProtocol1, MyProtocol2 {</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>< conforms MyProtocol2 ></span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func myMethod() -> String {</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""> <span class="Apple-tab-span" style="white-space:pre"> </span>return “..."</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""> <span class="Apple-tab-span" style="white-space:pre"> </span>}</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">```</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">Of course, there is no reason that tooling can’t replace “override” completely:</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">```</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">class MyClass: MyOtherClass, MyProtocol1, MyProtocol2 {</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>< conforms MyProtocol2 ></span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>< overrides TheParentClassOfMyOtherClass></span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func myMethod() -> String {</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""> <span class="Apple-tab-span" style="white-space:pre"> </span>return “..."</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class=""> <span class="Apple-tab-span" style="white-space:pre"> </span>}</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">```</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">Replace "<…>” with the navigable graphic of your choice and assume that user preferences would exist to show/hide these indicators.</span></div></div><div class=""><span style="font-kerning: none" class=""><br class=""></span></div><br class=""></div></div></blockquote><div><br class=""></div><div>My cut and paste error left out this part:</div><div><br class=""></div><div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">The roles of language and tooling in making code understandable is largely a matter of opinion. I personally like the current use of “override” since overriding is a common cause of serious programming errors and a mechanism for protecting against them should be built into the language and now, extended to overrides of protocol extensions.</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">It is interesting that adding “override” to structs and enums would help to open the door to true inheritance (not polymorphism) for structs and possibly even enums, if anyone knows of a use for that. This is a feature that I could have used on a few projects, but there are far more important features in the queue, and that discussion should probably wait until after Swift 4, if it happens at all.</span></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial; min-height: 14px;" class=""><span style="font-kerning: none" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; -webkit-text-stroke-color: rgb(0, 0, 0); -webkit-text-stroke-width: initial;" class=""><span style="font-kerning: none" class="">- Chris K</span></div><div class=""><span style="font-kerning: none" class=""><br class=""></span></div></div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class="">On Aug 24, 2016, at 11:13 AM, Christopher Kornher via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class=""><div class="">Requiring "override" when anything overrides a method defined in a protocol extension should be added - structure and enumerated included, of course.</div><div class=""><br class=""></div><div class="">Protocol extensions added inheritance to structs and enums and this should be made explicit.</div><div class=""><br class="">Sent from my iPad</div><div class=""><br class="">On Aug 24, 2016, at 12:55 AM, Charles Srstka via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><blockquote type="cite" class="">On Aug 24, 2016, at 1:20 AM, Robert Widmann <<a href="mailto:devteam.codafi@gmail.com" class="">devteam.codafi@gmail.com</a>> wrote:<br class=""></blockquote><div class=""><blockquote type="cite" class="">2016/08/23 20:52、Charles Srstka <<a href="mailto:cocoadev@charlessoft.com" class="">cocoadev@charlessoft.com</a>> のメッセージ:<br class=""><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class=""><div class=""><div class=""><div class=""><br class=""></div><blockquote type="cite" class=""><div class=""><blockquote type="cite" class="">On Aug 23, 2016, at 10:34 PM, Robert Widmann <<a href="mailto:devteam.codafi@gmail.com" class="">devteam.codafi@gmail.com</a>> wrote:<br class=""></blockquote><div class=""><blockquote type="cite" class=""><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">2016/08/23 15:29、Charles Srstka <<a href="mailto:cocoadev@charlessoft.com" class="">cocoadev@charlessoft.com</a>> のメッセージ:<br class=""><br class=""></div><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><blockquote type="cite" class="">On Aug 23, 2016, at 2:33 PM, Robert Widmann via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""></blockquote><div class=""><blockquote type="cite" class=""><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">2016/08/22 14:30、David Cordero via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> のメッセージ:<br class=""><br class=""></div><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><div dir="ltr" class=""><br class=""><div class=""><b class="">The problem:</b></div><div class="">At the moment, looking at the code of a class or a struct implementing a protocol, it is hard to know what methods are actually implementing the protocol and what other methods are just part of the code of the class or struct.<br class=""></div><div class=""><br class=""></div></div></div></blockquote><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">That seems like a feature, not a bug. Why should I as an author care whether a method contributes to a protocol conformance or not if the compiler can tell me that kind of information itself?</div></div></blockquote><div class=""><br class=""></div><div class="">Being able to reason about your code, what it does, and what it’s for is undesirable?</div></div></div></blockquote><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">That's not an answer to the question I asked. Why is this significant enough to warrant an entire keyword? The clutter of a whole keyword that does nothing but wait for a developer to make a source-compatible binary-breaking change to an interface does not seem worth it. Maybe you can convince me otherwise. </div></div></blockquote><div class=""><br class=""></div><div class="">Same reason overriding a class method warrants a keyword. It expresses the purpose more clearly, and allows the compiler to catch mistakes for us.</div><br class=""></div></div></blockquote><div class=""><br class=""></div><div class="">That's just it: The class of mistakes one can make by not being explicit about overrides is significantly more dangerous than the class of mistakes caused by dead code leftover from trimming protocols.</div></div></div></div></div></div></blockquote><div class=""><br class=""></div><div class="">I am in the middle of a large refactor of code that was originally Objective-C and then Swift written like Objective-C, to more idiomatic protocol-oriented Swift. I am finding that in Swift’s POP idiom, protocols with overrides are serving very nearly the same purpose that overrides were serving in the old design; hence, I don’t really think either is more or less dangerous than the other.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class=""><div class=""><div class=""><blockquote type="cite" class=""><div class=""><div class=""><blockquote type="cite" class=""><div class=""><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><div class=""><blockquote type="cite" class=""><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><div dir="ltr" class=""><div class="">```</div></div></div></blockquote><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><div dir="ltr" class=""><div class="">protocol MyProtocol {</div><div class=""> func myMethod() -> String</div><div class="">}</div><div class=""><br class=""></div><div class="">class MyClass: MyProtocol {</div><div class=""><br class=""></div><div class=""> <span class="Apple-converted-space"> </span><b class="">conform</b> func myMethod() -> String {</div><div class=""> return "Yuhuuu,I am conforming<span class="Apple-converted-space"> </span><a href="smb://o//" class="">\\o//</a>"</div><div class=""> }</div><div class=""><br class=""></div><div class=""> func whatever() {</div><div class=""> print("I am a boring method and I don't conform anything")</div><div class=""> }</div><div class="">}</div><div class="">```</div><div class=""><br class=""></div><div class="">It would be something similar to the current keyword `override` but for protocols. </div><div class=""><br class=""></div><div class="">Apart from improving code readability, It would allow the detection, in compilation time, of errors due to code evolution. For example redundant methods that no longer conform anything once the requirement is removed from the protocol for whatever reason.</div></div></div></blockquote><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">If you make a breaking change to a protocol like this, you should have gone through a deprecation cycle to indicate to your clients the appropriate changes you're going to make to the protocol. This aspect of the change seems to if not encourage, highlight, bad behavior.</div></blockquote></div><br class=""><div class="">What if it’s your own code and all the callers are internal? What if you’re still developing the protocol and haven’t released the API interface yet?</div></div></blockquote><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Then your concerns are local enough that you know where<span class="Apple-converted-space"> </span><i class="">all</i> implementations of the protocol lie and whether they require deletion or not. The point about deprecation cycles still stands in all the cases you mention. Just because the interface is private doesn't mean you can't take responsibility for keeping it as clean as you can.</div><br class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><div class=""><br class=""></div><div class="">Charles</div><div class=""><br class=""></div></div></blockquote><br class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">tl;dr It seems like all of this can be subsumed by us warning about dead code.</div></div></blockquote></div><br class=""><div class="">Did you look at my examples earlier in the thread? Neither of those would be caught by warning about dead code.</div></div></blockquote><div class=""><br class=""></div><div class="">The example involving the default implementation is most compelling, but it indicates that your proposed solution should focus on the protocol extension and not the implementing declaration. Perhaps reusing one of our existing keywords can help here</div><div class=""><br class=""></div><div class=""><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">protocol P {</span></div><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class=""> func foo() {}</span></div><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">}</span></div><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class=""><br class=""></span></div><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">extension P {</span></div><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class=""> default func foo() {}</span></div><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">}</span></div><div class=""><br class=""></div><div class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">struct S: P {}</span></div></div><div class=""><br class=""></div><div class="">Of course, this change would be potentially source-breaking either way - I don't like the sound of an "optional keyword”. </div></div></div></div></div></div></blockquote><div class=""><br class=""></div><div class="">I can come up with a similar example without the mistake being in the extension, though:</div><div class=""><br class=""></div><div class="">protocol P {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func foo() {}</div><div class="">}</div><div class=""><br class=""></div><div class="">extension P {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func foo() { print(“Default Behavior”) }</div><div class="">}</div><div class=""><br class=""></div><div class="">struct S: P {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func foo() { print(“Specific Behavior”) }</div><div class="">}</div><div class=""><br class=""></div><div class="">So far, so good. But now I realize that the original protocol needs an argument:</div><div class=""><br class=""></div><div class=""><div class="">protocol P {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>func foo(bar: String) {}</div><div class="">}</div><div class=""><br class=""></div><div class="">extension P {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>func foo(bar: String) { print(“Default Behavior; bar is \(bar)”) }</div><div class="">}</div><div class=""><br class=""></div><div class="">struct S: P {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>func foo() { print(“Specific Behavior”) } // Whoops, forgot to update this method, and now it won’t get called<span style="font-size: 11px;" class="">—</span>and we of course won’t see the carnage until runtime.</div><div class="">}</div></div><br class=""><blockquote type="cite" class=""><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class=""><div class=""><div class=""><div class="">Either way, we can all agree we need better diagnostics around these cases.</div></div></div></div></div></div></blockquote><br class=""></div><div class="">No doubt.</div><div class=""><br class=""></div>Charles<div class=""><br class=""></div></div></blockquote><blockquote type="cite" class=""><div class=""><span class="">_______________________________________________</span><br class=""><span class="">swift-evolution mailing list</span><br class=""><span class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a></span><br class=""><span class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class=""></div></blockquote></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class=""></div></div></blockquote></div><br class=""></body></html>