<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=""><blockquote type="cite" class="">On Aug 26, 2016, at 4:34 AM, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com" class="">xiaodi.wu@gmail.com</a>> wrote:<br class=""></blockquote><div><blockquote type="cite" class=""><br class="Apple-interchange-newline"><div class=""><span 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; float: none; display: inline !important;" class="">On Fri, Aug 26, 2016 at 4:24 AM, Charles Srstka<span class="Apple-converted-space"> </span></span><span dir="ltr" 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=""><<a href="mailto:cocoadev@charlessoft.com" target="_blank" class="">cocoadev@charlessoft.com</a>></span><span 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; float: none; display: inline !important;" class=""><span class="Apple-converted-space"> </span></span><span 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; float: none; display: inline !important;" class="">wrote:</span><br 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="gmail_extra" 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="gmail_quote"><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div style="word-wrap: break-word;" class=""><span class=""><blockquote type="cite" class="">On Aug 26, 2016, at 4:02 AM, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com" target="_blank" class="">xiaodi.wu@gmail.com</a>> wrote:<br class=""></blockquote><div class=""><blockquote type="cite" class=""><br class=""><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">That is not exactly what Brent was speaking of. We are talking about this scenario:</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">File A:</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">```</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">internal struct S {</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""> <span class="Apple-converted-space"> </span>func foo() { }</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">}</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">```</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">File B:</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">```</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">private protocol P {</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""> <span class="Apple-converted-space"> </span>func foo()</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">}</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">extension P {</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""> <span class="Apple-converted-space"> </span>func foo() { }</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">}</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">// With your proposal, I can't write the following line:</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">extension S : P { }</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">// In file A, S.foo() isn't overriding anything, so I can't add `override`</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">// But in file B, S can't conform to P,</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px;" class="">// because S.foo() isn't overriding P.foo() without `override` in file A</div></div></blockquote></div><br class=""></span><div class="">First of all, I cannot take credit for the proposal, as the thread was started by David, not me, so if the proposal is anyone’s, it’s his. With that said, what he proposes is:</div><span class=""><div class=""><br class=""></div><div class=""><blockquote type="cite" class=""><div class="">On Aug 22, 2016, at 4:30 PM, David Cordero via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:</div><br class=""><div class=""><div class=""><b class="">Proposal:</b></div><div class="">Adding a keyword to the methods conforming protocols. As an example please check the following piece of code which uses the keyword `conform` to explicitly indicate that `myMethod` is a method conforming a protocol.</div></div></blockquote></div><div class=""><div class=""><div class=""><br class=""></div></div></div></span><div class="">The wording here is that the keyword is needed for methods conforming to protocols. My reading of that is that:</div><div class=""><br class=""></div><div class="">File A:</div><div class=""><br class=""></div><div class="">protocol P {</div><span class=""><div class=""><span style="white-space: pre-wrap;" class=""> </span>func foo()</div><div class="">}</div><div class=""><br class=""></div><div class="">struct S: P {</div></span><div class=""><span style="white-space: pre-wrap;" class=""> </span>conform func foo() {</div><div class=""><span style="white-space: pre-wrap;" class=""> </span>// I am declared as conforming to P, so in adding this method I am doing so to conform to P. Thus, I need the keyword.</div><div class=""><span style="white-space: pre-wrap;" class=""> </span>}</div><div class="">}</div><div class=""><br class=""></div><div class="">- - whereas: - -</div><div class=""><br class=""></div><div class="">File A:</div><div class=""><br class=""></div><div class="">struct S {</div><div class=""><span style="white-space: pre-wrap;" class=""> </span>func foo() {</div><div class=""><span style="white-space: pre-wrap;" class=""> </span>// I am not declared as conforming to any protocol; I just think that being able to foo is an ability that I need to have.</div><span class=""><div class=""><span style="white-space: pre-wrap;" class=""> </span>}</div><div class="">}</div><div class=""><br class=""></div><div class="">File B:</div><div class=""><br class=""></div><div class="">private protocol P {</div><div class=""><span style="white-space: pre-wrap;" class=""> </span>func foo()</div><div class="">}</div><div class=""><br class=""></div></span><div class="">extension S: P {</div><div class=""><span style="white-space: pre-wrap;" class=""> </span>// The area of contention.</div><div class="">}</div><div class=""><br class=""></div><div class="">- - - - - -</div><div class=""><br class=""></div><div class="">The proposal doesn’t really mention what to do here, so we can argue a bit about it. There are multiple viewpoints one could take on this. A few could be:</div><div class=""><br class=""></div><div class="">1. The extension should get some kind of keyword, “retro” or “@retro” or something better-sounding that someone smarter than I comes up with.</div><div class=""><br class=""></div><div class="">2. The extension is unmarked, but declares foo() inside it with some sort of annotation to indicate that it represents a method that already exists.</div><div class=""><br class=""></div><div class="">3. Just leave the extension exactly as written, since it’s not declaring any methods, and thus doesn’t have to indicate what those nonexistent method declarations conform to.</div><div class=""><br class=""></div><div class="">I began this discussion leaning toward #1, but now I’m starting to consider #3, since the purpose of the keyword is to declare one’s intentions. The intentions of an empty extension that does nothing but conform to a protocol is actually quite clear; the methods have to be already declared somewhere else, or it makes no sense. At any rate, the “problem” in your scenario is entirely confined to File B, so if any annotations are necessary, that is where they belong. File A does not know about the protocol, it does not know that it is conforming to the protocol, and indeed, the protocol is none of File A’s business. So since File A is not intending to conform to the protocol, File A does not have to declare its intent to conform to the protocol. If we require that, it’s all in File B’s court.</div></div></blockquote><div class=""><br class=""></div><div class="">As I said, this discussion has already happened several times. I'm literally just repeating what people said eight months ago, six months ago, and four months ago. There's not a good answer to this and perhaps several other issues, which is why I don't see a way forward for the proposal. After all, I was the one proposing the same idea last winter, so I've had a few months to think about it.</div><div class=""><br class=""></div><div class="">If option (3) were allowed, then no keyword could ever be mandatory; it's always possible to refactor so that a conformance declaration is an empty extension. So we're back at an optional keyword, which has its own problems. This kind of thinking is how I've come to the conclusion that the status quo, with better diagnostics, is the least bad solution.</div></div></div></div></blockquote></div><div class=""><br class=""></div><div class="">Two responses to that thought:</div><div class=""><br class=""></div><div class="">1) In general, I look at these things under the assumption that most developers are not going to be making efforts to deliberately break the system, and not to try to expend excessive amounts of time in preventing them from doing so. Because really, just about *anything* can be worked around. I can work around the “override” keyword and override things without it, but that doesn’t mean that I think we should remove the “override” keyword. For that matter, just about *everything* in Objective-C was workaroundable, and usually rather trivially at that, but that didn’t make us all go back to typing everything as ‘id’ just because the explicit types could be spoofed.</div><div class=""><br class=""></div><div class="">2) Even if you disagree with everything I just said, that’s just as much an argument for option #1 as for the status quo.</div><br class=""><div class="">Charles</div><div class=""><br class=""></div></body></html>