<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 2:34 PM, 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=""><blockquote class="gmail_quote" 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; 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=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class=""><span class="">internal</span><span style="" class=""><span class="Apple-converted-space"> </span></span><span class="">struct</span><span style="" class=""><span class="Apple-converted-space"> </span>S {}</span></div><span class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><span class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class=""><span class="">private</span><span style="" class=""><span class="Apple-converted-space"> </span></span><span class="">protocol</span><span style="" class=""><span class="Apple-converted-space"> </span>P {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class=""> <span class="Apple-converted-space"> </span></span><span style="color: rgb(187, 44, 162);" class="">func</span><span class=""><span class="Apple-converted-space"> </span>foo()</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="">}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><span class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class=""><span class="">extension</span><span style="" class=""><span class="Apple-converted-space"> </span></span><span style="color: rgb(79, 129, 135);" class="">S</span><span style="" class="">:<span class="Apple-converted-space"> </span></span><span style="color: rgb(79, 129, 135);" class="">P</span><span style="" class=""><span class="Apple-converted-space"> </span>{</span></div></span><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class=""> <span class="Apple-converted-space"> </span></span><span style="color: rgb(187, 44, 162);" class="">func</span><span class=""><span class="Apple-converted-space"> </span>foo() {}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="">}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class="">- - - choose “Generated Interface” and you get: - - -</div><div style="margin: 0px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class=""><span class="">internal</span><span style="" class=""><span class="Apple-converted-space"> </span></span><span class="">struct</span><span style="" class=""><span class="Apple-converted-space"> </span>S {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="">}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><span class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><span class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class=""><span class="">extension</span><span style="" class=""><span class="Apple-converted-space"> </span></span><span style="color: rgb(79, 129, 135);" class="">S</span><span style="" class=""><span class="Apple-converted-space"> </span>{</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><span class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class=""><span style="" class=""> <span class="Apple-converted-space"> </span></span><span class="">internal</span><span style="" class=""><span class="Apple-converted-space"> </span></span><span class="">func</span><span style="" class=""><span class="Apple-converted-space"> </span>foo()</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="">}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class=""><span style="font-family: Helvetica; font-size: 12px;" class="">- - -</span></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class=""><span style="font-family: Helvetica; font-size: 12px;" class=""><br class=""></span></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class=""><span style="font-family: Helvetica; font-size: 12px;" class="">While the extension is visible, the fact that it adds conformance to P is not. Therefore, as far as code outside this file is concerned, there is no conformance to P.</span></span></div></div></div></div></div></blockquote><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><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="">That's correct, but why should the compiler accept the code in this file, when both S and P are visible, and S is not overriding default implementations in P as it should? </div></div></blockquote><div><br class=""></div><div>I am confused. Why should S, above, be required to override P’s default implementation of foo()?</div><br class=""><blockquote type="cite" class=""><div class=""><blockquote class="gmail_quote" 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; 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=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class=""><br class=""></span></div></div><span class=""><blockquote type="cite" 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="">In any case, you have not solved the problem, which has nothing to do with whether something is "reasonable to know": when a default implementation A is overridden by implementation B, implementation A may be visible only in a *more restricted* access scope than implementation B. (This is not the case with overriding superclass members in subclasses.) It can be perfectly "reasonable to know" about both A and B, but there is still no way you can indicate this knowledge by appending a keyword to the declaration for implementation B if the access scope for implementation A is unutterable where B is declared.</div></div></blockquote></span></div><div class=""><br class=""></div><div class="">Could you provide an example of code where this would present a problem?</div></div></blockquote><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=""><br class=""></div><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="">I'm still talking about the same example. How do you rationalize your statement that no keyword is needed because it's not "reasonable to know" about both S and P when compiling the file in which P is declared?</div></div></blockquote></div><br class=""><div class="">When compiling the file in which P is declared, you would add the keyword. Code outside this file that happened to define methods named foo() would not, since they would not be consciously conforming to the protocol.</div><div class=""><br class=""></div><div class="">Charles</div><div class=""><br class=""></div></body></html>