<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 2:22 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=""><div 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="">On Fri, Aug 26, 2016 at 1:53 AM, Charles Srstka<span class="Apple-converted-space"> </span><span dir="ltr" class=""><<a href="mailto:cocoadev@charlessoft.com" target="_blank" class="">cocoadev@charlessoft.com</a>></span><span class="Apple-converted-space"> </span>wrote:<br class=""><div class="gmail_extra"><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=""><div class=""><div class="h5"><blockquote type="cite" class="">On Aug 25, 2016, at 11:48 PM, 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 dir="ltr" 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 class="gmail_extra"><div class="gmail_quote">On Thu, Aug 25, 2016 at 11:05 PM, Charles Srstka<span class=""> </span><span dir="ltr" class=""><<a href="mailto:cocoadev@charlessoft.com" target="_blank" class="">cocoadev@charlessoft.<wbr class="">com</a>></span><span class=""> </span>wrote:<br class=""><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 25, 2016, at 10:24 PM, 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=""><span 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; float: none; display: inline !important;" class="">Yes, and it's covered in those previous threads. In brief, not all retroactive modeling involves extending a type:</span><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="">* A vendor supplies you with a closed-source library with a struct S that conforms to standard library 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=""><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="">* Protocol P requires a method named foo(), so struct S has its own implementation of 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=""><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="">* You extend protocol P by adding a new default implementation of 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=""><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="">This cannot be done if a keyword is required for overriding a default implementation. There is also nowhere for you to append any sort of "retro" keyword anywhere, because no part of your own code extends S in any way.</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="">Please, please take the time to study the previous threads; we should not be re-playing existing discussions four or five times on this list.</div></div></blockquote></div><br class=""></span><div class="">How is this a problem, though? The implementation of foo() in S will not break, because it’s already been compiled in. The change will only affect code that is subsequently compiled with your extension of P in place. And it’ll be doing its job; making sure that your code to implement the protocol is there deliberately, and preventing you from accidentally mistyping the method name and thus silently failing to override the default implementation.</div></div></blockquote><div class=""><br class=""></div><div class="">So you're saying that the compiler should let you compile your extension of P, even though it knows that the default implementation of `foo()` is not explicitly overridden by S. Fine.</div><div class="">Now suppose the library is not closed-source; you're including it in your project and compiling it along with your own code. Are you supposed to fork the library?</div></div></div></div></div></blockquote></div><br class=""></div></div><div class="">Even if the library is open-source, you'll presumably be building in as its own target, which will be including only library code and not your extension, and linking it into the application in a later stage of the build process.</div></div></blockquote><div class=""><br class=""></div><div class="">I made the same argument eight months ago:</div><div class=""><br class=""></div><div class=""><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;">><i class=""><span class="Apple-converted-space"> </span>Another option might be to allow imported definitions to be used by a conformance without the `override` marking to support retroactive modeling while requiring definitions in the same module as the conformance to explicitly specify the `override`.<br class=""></i></blockquote><div class=""><br class=""></div><div class=""> But Brent Royal-Gordon had a good point: </div><div class=""><br class=""></div><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;"><i class=""></i>But the same problem exists if you want to do this to `internal` types using a `private` protocol. There you *could* make the protocol `internal` and call `override` in all the right places, but if the protocol is an implementation detail of one particular file, why should you?</blockquote></div></div></div></div></div></blockquote></div><br class=""><div class="">If the protocol is private, than to code outside that file, the protocol effectively doesn’t exist, since code in protocol extensions is statically dispatched (this is also true to code in your hypothetical library). So no need for “override” there.</div><div class=""><br class=""></div><div class="">If the protocol is internal, than code elsewhere in your app can see it, and thus they should have to override, for the same reason that if you added a superclass method that some subclass was already using, you’d need to add “override”.</div><div class=""><br class=""></div><div class="">Charles</div><div class=""><br class=""></div></body></html>