<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="">Hey Brad<div class=""><br class=""></div><div class="">+1 I think this will make delegate controller pattern a lot more clean and readable.</div><div class=""><br class=""></div><div class="">I was thinking about other areas where this can be useful, and I thought it will be great for property injection from parent controller to children.</div><div class=""><br class=""></div><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class=""><div class="" style="margin: 0px; line-height: normal; font-family: Menlo;"><div class="" style="margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ParentController{</span></div><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">protocol</span><span style="font-variant-ligatures: no-common-ligatures" class=""> Injection: </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures" class="">{</span></div><p style="margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">override</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> prepareForSegue(segue: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">UIStoryboardSegue</span><span style="font-variant-ligatures: no-common-ligatures" class="">, sender: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">AnyObject</span><span style="font-variant-ligatures: no-common-ligatures" class="">?){</span></div><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> childVC = segue.destinationViewController </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">as</span><span style="font-variant-ligatures: no-common-ligatures" class="">? Injection</span></div><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> ...</span></div><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; color: rgb(79, 129, 135);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> ChildController: </span><span style="font-variant-ligatures: no-common-ligatures" class="">ParentController</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span><span style="font-variant-ligatures: no-common-ligatures" class="">Injection</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">{</span></div><p style="margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal;" class=""><br class=""></div></span></div></div></div></div></div></div><div class=""><table class="js-file-line-container highlight tab-size" data-tab-size="8" style="box-sizing: border-box; border-spacing: 0px; border-collapse: collapse; tab-size: 8; color: rgb(51, 51, 51); font-family: Helvetica, arial, nimbussansl, liberationsans, freesans, clean, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 13px;"><tbody style="box-sizing: border-box;" class=""></tbody></table><div class=""><table class="js-file-line-container highlight tab-size" data-tab-size="8" style="box-sizing: border-box; border-spacing: 0px; border-collapse: collapse; tab-size: 8; color: rgb(51, 51, 51); font-family: Helvetica, arial, nimbussansl, liberationsans, freesans, clean, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 13px;"><tbody style="box-sizing: border-box;" class=""><tr style="box-sizing: border-box;" class=""><td id="file-nestedprotocol-swift-L5" class="blob-num js-line-number" data-line-number="5" style="box-sizing: border-box; padding: 0px 10px; width: 50px; min-width: 50px; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 12px; line-height: 18px; color: rgba(0, 0, 0, 0.298039); text-align: right; white-space: nowrap; vertical-align: top; cursor: pointer; -webkit-user-select: none; border-style: solid; border-color: rgb(238, 238, 238); border-width: 0px 1px 0px 0px;"></td></tr></tbody></table><br class=""></div></div><div class="">Does this make sense?</div><div class=""><br class=""></div><div class="">-Krishna</div><div class=""><br class=""></div><div class=""><div><blockquote type="cite" class=""><div class="">On Apr 28, 2016, at 10:45 PM, Brad Hilton 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="">Type nesting allows some convenient and straightforward semantics that we see inside the Swift standard library such as views on String like String.CharacterView, String.UnicodeScalarView, etc. However a protocol cannot be nested in a type and gives a non-obvious error that the “Declaration is only valid at file scope.” Just as other nested types allow proper contextual scoping, a nested protocol could make a lot sense for a number of patterns. For example, there are many “Delegate” protocols throughout the Cocoa frameworks. Here’s a controller/delegate pattern before and after type nesting:<div class=""><div class=""><br class=""></div><div class=""><div style="margin: 0px; line-height: normal; font-family: Menlo;" class=""><div style="margin: 0px; line-height: normal; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">// Without type nesting</span></div><div style="margin: 0px; line-height: normal; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">protocol</span><span style="font-variant-ligatures: no-common-ligatures" class=""> MyControllerDelegate : </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures" class=""> MyController {</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></div><div style="margin: 0px; line-height: normal; color: rgb(79, 129, 135);" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">weak</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> delegate: </span><span style="font-variant-ligatures: no-common-ligatures" class="">MyControllerDelegate</span><span style="font-variant-ligatures: no-common-ligatures;" class="">?</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; line-height: normal; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">// With type nesting</span></div><div style="margin: 0px; line-height: normal; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures" class=""> MyController {</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">weak</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> delegate: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Delegate</span><span style="font-variant-ligatures: no-common-ligatures" class="">?</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">protocol</span><span style="font-variant-ligatures: no-common-ligatures" class=""> Delegate : </span><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal; min-height: 14px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-family: Helvetica;" class="">Though the change is mostly semantics, it does allow an explicit association between My Controller and the Delegate instead of only a named association. It also cleans up the module name space like other nested types and makes associated protocols more discoverable in my opinion. </span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-family: Helvetica;" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-family: Helvetica;" class="">I’d love to hear everyone’s thoughts.</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-family: Helvetica;" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-family: Helvetica;" class="">Brad Hilton</span></div></div></div></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=""></div></body></html>