<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="">Hi Rick,<div class=""><br class=""></div><div class="">I think you’re looking for something like this? Assuming when you say “return” in your bullet spec you mean assign-in-place since we’re talking about +=</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> +=<T>(lhs: </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">inout</span><span style="font-variant-ligatures: no-common-ligatures" class=""> [</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">T</span><span style="font-variant-ligatures: no-common-ligatures" class="">]?, rhs: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">T</span><span style="font-variant-ligatures: no-common-ligatures" class="">]?) {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">switch</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (lhs,rhs) {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">,</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">nil</span><span style="font-variant-ligatures: no-common-ligatures" class="">): </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #008f00" class="">// no-op whether lhs is nil or not when rhs is</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">nil</span><span style="font-variant-ligatures: no-common-ligatures" class="">,</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">?): lhs = rhs </span><span style="font-variant-ligatures: no-common-ligatures; color: #008f00" class="">// lhs of nil gets replaced</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">?,let rhs?): lhs!.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">append</span><span style="font-variant-ligatures: no-common-ligatures" class="">(contentsOf: rhs) </span><span style="font-variant-ligatures: no-common-ligatures; color: #008f00" class="">// neither nil: append in-place</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class="">(you could make rhs generic over sequences too but then you don’t get automatic handling of subclasses of T on the rhs)</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class="">But it’s probably not a good idea to overload += like this since the extra handling of nils, especially on the lhs, is a bit out of the expected behavior for += and could backfire if you accidentally used it somewhere you didn’t expect. So maybe make it a method with a new name, like:</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">extension</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Optional</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">where</span><span style="font-variant-ligatures: no-common-ligatures" class=""> Wrapped: RangeReplaceableCollection {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">mutating</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> maybeAppend(others: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Wrapped</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Iterator.Element]?) {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">switch</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">,others) {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">,</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">nil</span><span style="font-variant-ligatures: no-common-ligatures" class="">): </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">return</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">nil</span><span style="font-variant-ligatures: no-common-ligatures" class="">,let x?): </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Wrapped</span><span style="font-variant-ligatures: no-common-ligatures" class="">(x)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">?,let x?): </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">!.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">append</span><span style="font-variant-ligatures: no-common-ligatures" class="">(contentsOf: x)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><br class=""></div><div class=""><div><blockquote type="cite" class=""><div class="">On Oct 20, 2016, at 5:17 PM, Rick Mann via swift-users <<a href="mailto:swift-users@swift.org" class="">swift-users@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">When working with URLComponents query items, it would be nice to write code like this:<br class=""><br class="">var oqi: [URLQueryItem]? = [..., ..., ...]<br class=""><br class="">var comps = URLComponents(…)<br class="">comps.queryItems += oqi<br class=""><br class="">The problem is that queryItems is [URLQueryItem]?, and so I can't just append. I'd like to write a version of += that:<br class=""><br class="">• Takes an LHS of [URLQueryItems]?, RHS of [things possibly derived from URLQueryItem]?<br class="">• if LHS != nil, make an array of LHS, and optionally append RHS, and return that<br class="">• if LHS == nil && RHS != nil, return RHS<br class="">• If both are nil, return nil<br class=""><br class="">I'd like to do this in a generic way that works for any type on the left and possibly-dervied types on the right.<br class=""><br class="">-- <br class="">Rick Mann<br class=""><a href="mailto:rmann@latencyzero.com" class="">rmann@latencyzero.com</a><br class=""><br class=""><br class="">_______________________________________________<br class="">swift-users mailing list<br class="">swift-users@swift.org<br class="">https://lists.swift.org/mailman/listinfo/swift-users<br class=""></div></div></blockquote></div><br class=""></div></body></html>