<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=""><div class="">Is there a reason that adding a “retro” keyword on extensions meant to retroactively apply a protocol is unacceptable?</div><div class=""><br class=""></div><div class="">Charles</div><br class=""><div><blockquote type="cite" class=""><div class="">On Aug 25, 2016, at 6:44 PM, Xiaodi Wu 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=""><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="">Chris, as I wrote above, this idea has been discussed previously on several occasions, and the principal reason why it has been abandoned each time is that it cannot accommodate retroactive modeling. I'll refer you again to three previous threads discussing this and closely related matters:</span></div></blockquote></div><br class=""></body></html>