<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 22, 2017, at 4:53 PM, Dave Abrahams via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><div class=""><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="">Sent from my iPad</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=""><br class="">On Jan 22, 2017, at 3:15 PM, Chris Lattner <<a href="mailto:clattner@nondot.org" class="">clattner@nondot.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" 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-size-adjust: auto; -webkit-text-stroke-width: 0px;" class=""><div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jan 20, 2017, at 12:22 PM, Dave Abrahams 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=""><div class="Singleton"><blockquote type="cite" class="" 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;"><br class="">Yeah, maybe there's a more general language feature that could replace 'fallthrough' here. Instead<br class="">of labelling cases, we could support a 'reswitch' statement that redispatches the switch to the case<br class="">matching the operand:<br class=""><br class=""> switch some_value {<br class=""> case .REFINED:<br class=""> if !validate(some_value) { return NULL }<br class=""> reswitch .BASE<br class=""><br class=""> case .BASE:<br class=""> handle_enum_value();<br class=""> }<br class=""></blockquote><br class="" 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;"><span class="" 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;">We should just call a spade a spade and spell that "goto" ;-)</span><br class=""></div></div></blockquote><br class=""></div><div class="">Goto has traditionally been used for unstructured control flow, but this form is still fully structured. You cannot produce irreducible loops, jump into scopes, over declarations, etc.</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><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="">It would be useful to know the technical definition of "structured." The fact is that there's a large category of sensible goto-like jumps that we probably want to allow and I see no advantage to giving them all distinct names. I don't believe users will distinguish them. We already have "break looplabel" and, aside from the label being in the wrong place, it's effectively a goto. It seems to me we should just have goto and either prohibit the troublesome uses or give them reasonable semantics.</span><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 class=""><br class=""></div><div class="">I could live with "break" as well as "goto", but it feels a bit like it's pretending to be something it isn't, and there's the source compatibility problem with the label position.</div><div class=""><br class=""></div></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="">-Dave</div></div></blockquote><br class=""></div><div>I always assumed structured control flow means control only jumps to approved points, not arbitrary statements. Implicitly this is jumping out of a scope to a less-nested scope but never into a more-nested scope.</div><div><br class=""></div><div>Swift takes this even further: you are limited to early exit of control flow. That’s a lot more restrictive than arbitrary goto.</div><div><br class=""></div><div><br class=""></div><div>Russ</div><br class=""></body></html>