<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 May 16, 2017, at 12:32 PM, Nevin Brackett-Rozinsky via swift-users <<a href="mailto:swift-users@swift.org" class="">swift-users@swift.org</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; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">There is not.</span><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; 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; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">At some point in the future, I believe the plan is to eventually allow default implementations to be written in-line within the protocol declaration itself. In other words, the fact that default implementations currently must appear in extensions, is a temporary limitation that has not yet been a priority to address.</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; 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; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Once we gain the ability to define default implementations within protocols themselves, rather than extensions, then your use-case will “just work” (at least as long as you control the protocol anyway). I wouldn’t hold my breath though, as that behavior will not appear this year, and the plans for next year have not been hashed out yet.</div></div></blockquote></div><br class=""><div class="">Even that won’t completely solve the problem, though, because:</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=""><span class="Apple-tab-span" style="white-space:pre"> </span>// default implementation</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</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() {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>// overriden implementation</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</div><div class="">}</div><div class=""><br class=""></div><div class="">If foo is refactored here, S will start getting the wrong implementation of it, silently, with no warning.</div><div class=""><br class=""></div><div class="">People have tried to bring up proposals to add some sort of “override”-like keyword for protocols on swift-evolution a bunch of times, but it always gets shouted down by certain members of the group, so we’re probably permanently stuck with this situation where a supposedly “protocol-oriented” language is not safe to use with protocols.</div><div class=""><br class=""></div><div class="">Charles</div><div class=""><br class=""></div></body></html>