<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 Jun 28, 2016, at 2:18 PM, Jonathan Hull 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=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">One more question on this.<div class=""><br class=""></div><div class="">How would we handle the opt-out safety for people who are intentionally trying to create an infinite loop?</div><div class=""><br class=""></div><div class="">I don’t think we can make .until() safely lazy for iterators which have reference semantics and are destructive single-pass, so it has to be eager. </div></div></div></blockquote><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">If .until() is eager, then .until(false) will fall into an infinite loop before the for-in loop is even run. </div></div></div></blockquote><div><br class=""></div><div>This is an argument against a library solution if iterators have reference semantics. Any solution that requires eager behavior is not a good solution.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div><div class="">Maybe there just a way to plug an iterator/sequence directly in, and then silence the warning? or we could do for-in-until…</div></div></div></blockquote><div> </div><div>I don’t think this should be a warning that can be silenced. I think you are uncovering good reasons to go with a language supported solution.</div><div><br class=""></div><div>This wouldn’t need to happen in Swift 3. There have been other cases where we have adopted a “break it now in anticipation of making it better in the future” policy. If we conclude that a language solution is warranted and can’t get it into Swift 3 that is ok IMO. It is still possible to manually iterate infinite sequences. This wouldn’t be that big a deal given that it is relatively infrequent.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Jon</div><div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jun 28, 2016, at 10:51 AM, Dave Abrahams <<a href="mailto:dabrahams@apple.com" class="">dabrahams@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><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-stroke-width: 0px;" class=""><blockquote type="cite" class=""><br class="">This is a reasonable structure, but there are important details missing.<br class=""><br class="">1. Presumably these are all for-in-able. What makes something<br class=""> for-in-able?<br class=""></blockquote><br class="">I would think the potentially infinite should require for-in-until<br class="">(even if you explicitly set until to false to create an infinite<br class="">loop), but collection would allow for-in (with optional until). That<br class="">way you have to acknowledge the possibility of an infinite<br class="">sequence/iterator.<br class=""></blockquote><br 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=""><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="">Are you proposing a new language feature? We could also do this with</span><br 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 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=""><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=""> for i in allIntegers.until(isPrime)</span></div></div></blockquote></div><br class=""></div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></blockquote></div><br class=""></body></html>